Mathematics Chapter 15 Introduction To Graphs
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    NCERT Solution For Class 8 Mathematics

    Introduction To Graphs Here is the CBSE Mathematics Chapter 15 for Class 8 students. Summary and detailed explanation of the lesson, including the definitions of difficult words. All of the exercises and questions and answers from the lesson's back end have been completed. NCERT Solutions for Class 8 Mathematics Introduction To Graphs Chapter 15 NCERT Solutions for Class 8 Mathematics Introduction To Graphs Chapter 15 The following is a summary in Hindi and English for the academic year 2021-2022. You can save these solutions to your computer or use the Class 8 Mathematics.

    Question 1
    CBSEENMA8003493

    The following graph shows the temperature of a patient in a hospital, recorded every hour.
    (a) What was the patient’s temperature at 1 p.m.?
    (b) When was the patient’s temperature 38.5° C?
    (c) The patient’s temperature was the same two times during the period given. What were these two times?
    (d) What was the temperature at 1.30 p.m.? How did you arrive at your answer?
    (e) During which periods did the patients’ temperature showed an upward trend?


     

    Solution

    (a) The patient’s temperature at 1 p.m. was 36.5°.
    (b) The patient's temperature 38.5° C was at 12 noon.
    (c) The patient's temperature was same at 1 p.m. and 2 p.m.
    (d) The patient’s temperature at 1:30 p.m. was 36.5° C [because the temperature of the patient was constant (i.e. 36.5° C) from 1 p.m. to 2 p.m.].
    (e) The temperature of patient showed an upward trend during 9 a.m to 10 a.m. to 11 a.m. and 2 p.m. to 3 p.m.

    Question 2
    CBSEENMA8003495

    The following line graph shows the yearly sales figures for a manufacturing company.
    (a) What were the sales in (i) 2002 and (ii) 2006?
    (b) What were the sales in (i) 2003 and (ii) 2005?
    (c) Compute the difference between the sales in 2002 and 2006.
    (d) In which year was there the greatest difference between the sales as compared to its previous year?

    Solution

    (a) (i) Company's sale in 2002 was Rs 4 crores.
         (ii) Company’s sale in 2006 was Rs 8 crores.
    (b) (i) Company’s sale in 2003 was Rs 7 crores.
          (ii) Company’s sale in 2005 was Rs 10 crores.

    (c)  Difference between the sales in 2002 and 2006 = [Rs 8 crores] – [Rs 4 crores]
          = Rs 4 crores

    (d) The greatest difference between the sales of two consecutive years 2004 and 2005.

    Question 3
    CBSEENMA8003496

    For an experiment in Botany, two different plants, plant A and B were grown under similar laboratory conditions. Their height were measured at the end of each week for 3 weeks. The results are shown by the following graph.

    (a) How high was plant A after (i) 2 weeks and (ii) 3 weeks?
    (b) How high was plant B after (i) 2 weeks and (ii) 3 weeks?
    (c) How much did plant A grow during the 3rd week?
    (d) How much did plant B grow from the end of the 2nd week to the end of the 3rd week?
    (e) During which week did plant A grow most?
    (f) During which week did plant B grow least?
    (g) Were the two plants of the same height during any week shown here? Specify.

    Solution

    (a) (i) After 2 weeks: The plant A was 7 cm high. (ii) After 3 weeks:The plant A was 9 cm high.
    (b) (i) After 2 weeks: The plant B was 7 cm high. (ii) After 3 weeks: The plant B was 10 cm high.
    (c) During the 3rd week, the plant grew (9 cm – 7 cm), i.e. 2 cm.
    (d) The plant B grew 10 cm – 7 cm = 3 cm from the end of 2nd week to the end of the 3rd week.
    (e) The growth of the plant A:
    During the 1st week = 1 cm – 0 cm = 1 cm, During the 2nd week = 7 cm – 1 cm = 6 cm, During the 3rd week = 9 cm – 7 cm = 2 cm. Thus, during the 2nd week, the plant A grew the must.
    (f) The growth of the plant B during:
    the 1st week = 1 cm – 0 cm = 1 cm
    the 2nd week = 7 cm – 1 cm = 6 cm
    the 3rd week = 10 cm – 7 cm = 3 cm
    Thus, the plant-B grew the least in the first week.
    (g) Both the plants have shown almost the same height at the end of the 2nd week.

    Question 4
    CBSEENMA8003498

    The following graph shows the temperature forecast and the actual temperature for each day of a week.
    (a) On which days was the forecast temperature the same as the actual temperature?
    (b) What was the maximum forecast temperature during the week?
    (c) What was the minimum actual temperature during the week?
    (d) On which day did the actual temperature differ the most from the forecast temperature?

    Solution

    (a) The forecast temperature was the same as the actual temperature on Tuesday, Friday and Sunday.
    (b) The maximum forecast temperature during the week was 35° C.
    (c) The maximum actual temperature during the week was 15° C.
    (d) Difference between the actual temperature and the forecast temperature on
    Monday = 17.5° C – 15° C = 2.5° C
    Tuesday = 20.5° C – 20° C = 0.5° C
    Wednesday = 30.0° C – 25° C = 5° C
    Thursday = 22.5° C – 15° C = 7.5° C
    Friday = 15° C – 15° C = 0° C
    Saturday = 30° C – 25° C = 5° C 
    Sunday = 35° C – 35° C = 0° C
    Thus, the maximum difference was on Tuesday.

    Question 5
    CBSEENMA8003503
    Question 6
    CBSEENMA8003504

    Population (in thousands) of men and women in a village in different years.


    Solution
    Linear graph showing population of men and women in a village in different years:
    Question 7
    CBSEENMA8003505

    A courier-person cycles from a town to a neighbouring suburban area to deliver a parcel to a merchant. His distance from the town at different times is shown by the following graph.
    (a) What is the scale taken for the time axis?
    (b) How much time did the person take for the travel?
    (c) How far is the place of the merchant from the town?
    (d) Did the person stop on his way? Explain.
    (e) During which period did he ride fastest?

    Solution
    (a) The time is taken along the x-axis. The scale along x-axis is 4 units = 1 hour 
    (b) Total travel time = 8 a.m. to 11:30 a.m. = 3 1 half space hours
    (c) Distance of the merchant from the town = 22 km.
    (d) Yes, the stopage time = 10:00 a.m. to 10.30 a.m.
    (e) His fast ride is between 8:00 a.m. and 9:00 a.m.
    Question 8
    CBSEENMA8003506

    Can there be a time-temperature graph as follows? Justify your answer.


    Solution

    In case of (iii), there are an infinite number of temperature at the same time which is not possible.
    ∴   Case (iii) does not represent a time-temperature graph.

    Question 12
    CBSEENMA8003510

    Plot the following points on a graph sheet. Verify if they lie on a line:
    (a) A (4, 0), B(4, 2), C(4, 6), D(4, 2.5)
    (b) P(1, 1), Q(2, 2), R(3, 3), S(4, 4)
    (c) K(2, 3), L(5, 3), M(5, 5), N(2, 5)

    Solution

    In each case we draw the x-axis and the y-axis and plot the given point.
    (a) on plotting the points A(4, 0), B(4, 2), C(4, 6) and D(4, 2.5) and then joining them we find that they all lie on the same line.
    (b) On plotting the points P(1, 1), Q(2, 2), R(3, 3) and S(4, 4) and then joining them we find that they all lie on the same line.
    (c) Plotting the points k(2, 3) L(5, 3), M(5, 5) and N(2, 5) and joining them we find that all of them do not lie on the same line.

    Question 13
    CBSEENMA8003511

    Draw the line passing through (2, 3) and (3, 2). Find the coordinates of the points at which this line meets the x-axis and y-axis.

    Solution
    On plotting the points A(2, 3) and B(3, 2) and joining them, draw a line. On extending the line meets the x-axis at c(5, 0) and the y-axis at D(0, 5).
    Question 14
    CBSEENMA8003512

    Write the coordinates of the vertices of each of these adjoining Figures.

    Solution

    (i)  The co-ordinates of :
              O are (0, 0)
              A are (2, 0)
              B are (2, 3)
              C are (0, 3)
    (ii)  The co-ordinates of :
               P are (4, 3)
               Q are (6, 1)
               R are (6, 5)
               S are (4, 7)
    (iii) The co-ordinates of:
                K are (10, 5)
                L are (7, 7)
                M are (10, 8)

    Question 16
    CBSEENMA8003515

    The number of litres of petrol you buy to fill a car’s petrol tank will decide the amount you have to pay. Which is the independent variable here? Think about it.

    Solution

    Since, quantity of petrol is a need whereas the amount of money is linked with the quantity of petrol.
    Petrol is the independent variable.

    Question 17
    CBSEENMA8003517

    The following table gives the quantity of petrol and its cost.


    Plot a graph to show the data.
    Use the graph to find how much petrol can be purchased for Rs 800.

    Solution

    We draw axes and take a suitable scale on both the axes. To draw the graph, we take the following steps:
    I. Mark the number litres of petrol along the horizontal axis.
    II. Mark the cost of petrol (in rupees) along the y-axis.
    III. Now, we plot the given points, i.e.
    (10, 500); (15, 750); (20, 1000); (25, 1250)
    IV. Join the points.
    We find that the graph is a straight line.

    Yes, we can find the quantity of petrol to be got in Rs 800, for this take a point on the y-axis (0,800). Through A draw BC parallel to x-axis to meet the graph at B. Now from B, draw BC Perpendicular x-axis.
    As C corresponds to (16, 0).
    Thus, 16 litre petrol can be bought for Rs 800.

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    Question 18
    CBSEENMA8003518

    Draw the graphs for the following tables of values, with suitable scales on the axes,
     Cost of apples


    Solution

    I. Draw x-axis and y-axis mutually perpendicular to each other.
    II. Take a suitable scale.
    III. Take the number of apples along the x-axis and mark the cost (in Rs) along the y-axis.
    IV. Plot the points (1, 5), (2, 10), (3, 15), (4, 20) and (5, 25).
    V. Joint the points.
    We obtain the graph a straight line.

    Question 19
    CBSEENMA8003520

    Draw the graphs for the following tables of values, with suitable scales on the axes,
    Distance travelled by a car


    (i) How much distance did the car cover during the period 7.30 a.m. to 8 a.m.?
    (ii) What was the time when the car had covered a distance of 100 km since it’s start?



    Solution

    Steps:
    I.  Draw the axis.
    II. Choose suitable scale along x-axis and along y-axis.
    III.Mark time (in hours) along x-axis and distance (in km) along y-axis
    IV.Plot the points (6, 40) (7, 80), (8, 120) and (9, 160).
    V. By joining the points we get the required graph.

    (i) In the graph, draw a perpendicular at the point indicating 7:30 a.m. on the x-axis such that it meets the graph at A. From A draw a line parallel to x-axis to meet y-axis at 100 km.
    ∴ Distance travelled between 7:30 a.m. and 8:00 a.m.
    = 120 km – 100 km
    = 20 km
    (ii) 7:30 a.m.

     
    Question 20
    CBSEENMA8003523

    Draw the graphs for the following tables of values, with suitable scales on the axes,
    Interest on deposits for a year.

    (i) Does the graph pass through the origin?
    (ii) Use the graph to find the interest on Rs 2500 for a year.
    (iii) To get an interest of Rs 280 per year, how much money should be deposited?



     


    Solution

    Steps:
    I. Draw axes.
    II. Take appropriate scale on x-axis and y-axis.
    III. Mark the deposits along the x-axis.
    IV. Mark the interest along the y-axis.
    V. Plot the point (1000, 80) (2000, 160), (3000, 240), (4000, 320) and (5000, 400).
    VI. Join the points and get the graph.

     Now from the graph, we have:
    (i) Yes, it passes through the origin.
    (ii) From the graph, the interest on Rs 2500 is Rs 200.
    (iii) From the graph an interest of Rs 280 can be got by depositing Rs 3500.

    Question 21
    CBSEENMA8003528

    Draw a graph for the following.


    Is it a linear graph?

    Solution

    Taking the side of the square along the x-axis and the perimeter along the y-axis and plotting the points (2, 8), (3, 12), (3.5, 14), (5, 20) and (6, 24), we get the required graph as a straight line.
    ∴ This graph is a linear graph.

    Question 22
    CBSEENMA8003531

    Draw a graph for the following:


    Is it a linear graph?



    Solution
    Taking the side of the square along the x-axis and area (in cm2) along the y-axis, we can draw the required graph by plotting the points (2, 4), (3, 9), (4, 16), (5, 25) and (6, 36) as shown in the following figure.

    ∴ The graph is not a straight line.
    ∴ It is not a linear graph.


    Question 23
    CBSEENMA8003532
    Question 27
    CBSEENMA8003537

    Draw a ‘time-distance’ graph for the following.

    Solution

    Solution not provided.

    Question 28
    CBSEENMA8003538

    Draw the points (5, 4) and (4, 5). Do they represent the same point?

    Solution

    From the graph, we observe that the points (5, 4) and (4, 5) are different, i.e. they represent different points.
    Question 29
    CBSEENMA8003539

    Draw a line passing through (2, 1) and (1, 2). Find the coordinates of the points at which this line meets the x-axis and y-axis.

    Solution

    On plotting the given points A(1, 2) and B(2, 1) on the same graph and joining them, we get a straight line AB. When we extend the line AB on both sides, we find that it intersects the x-axis at C(3, 0) and the y-axis at D(0, 3).
    Question 30
    CBSEENMA8003540

    Write the coordinates of the vertices of the following figure.

    Solution

    From the figure, we have
    The co-ordinates of P are (0, 4). The co-ordinates of Q are (5, 5). The co-ordinates of R are (10, 3). The co-ordinates of S are (10, 2). The co-ordinates of T are (8, 0).

    Question 31
    CBSEENMA8003541
    Question 32
    CBSEENMA8003542

    Plot the following points on a graph sheet. Verify if they lie on line.
    A(5, 0), B(5, -2), C(5, 4), and D(5, 6).

    Solution

    On plotting the given points A(5, 0), B(5, -2), C(5, 4) and D(5, 6) and joining them, we find that they lie on the line segment BD.
    Question 33
    CBSEENMA8003543

    Draw the graph for the following data:

    Solution
    Solution not provided.
    Ans. By taking the ‘side of the square’ along the x-axis and the corresponding perimeters along the y-axis, we plot the points (1,4), (2, 8), (3, 12) and (4, 16). On joining these points, we get the required graph, which is a straight line.
    Question 34
    CBSEENMA8003544

    Draw the graph for the following table of values of time (in hours) and distances (in km) covered by a car. From the graph, find:
    (i) The distance covered by the car during the period 7:00 to 8 :00.
    (ii) At what time the car would have covered 180 km?


    Solution

    By plotting the points (7:00, 60), (8:00, 120), (9:00, 180) and (10:00, 240), we get a straight line.

    (i) Distance covered during 7:00 and 8:00 = (180 – 120) km = 60 km.
    (ii) From the graph the car would have covered 180 km at 9:00.

    Question 35
    CBSEENMA8003545

    Find the coordinates of the vertices of ∆ABC given in graph. Draw a triangle by taking vertices as A(5, 2), B(1, 2) and C(1, 5).

    Solution

    From the graph, the vertices of ∆ABC are: A, B and C. We find that
    The co-ordinates of A are (2, 5).
    The co-ordinates of B are (2, 1).
    The co-ordinates of C are (5, 1).
    The required triangle with vertices as A(5, 2), B(1, 2) and C(1, 5) is given in the following graph.

    Question 36
    CBSEENMA8003546

    Following graph describes the movement of a car from a town A to town D. Study the graph and answer the following questions:

    (i) What is the distance between town A and town D?
    (ii) When did the car start from town A?
    (iii) Where did the car stop and for what duration?
    (iv) How long did it take to go from town C to town D?



    Solution

    (i) The distance between the town A and town D is 500 km - 100 km = 400 km.
    (ii) The car started from the town A at 5 a.m.
    (iii) The car stopped at town B for 1 hour (7 a.m. to 8 a.m.).
    (iv) The car look 2 hours to reach from town C to town D.

    Question 37
    CBSEENMA8003547

    Read the following ‘time-temperature’ graph of a place and answer the questions given below.
    (i) What was the temperature at 7 a.m.?
    (ii) When the temperature was maximum?


    (iii) When was the temperature 40°C?
    (iv) During which period, the temperature remained constant?

    Solution

    (i) At 7 a.m., the temperature was 34° C.
    (ii) The maximum temperature (44° C) was at 11 a.m.
    (iii) At 10 a.m., the temperature was 40° C.
    (iv) The temperature remained constant during 8 a.m. to 9 a.m.

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    Question 40
    CBSEENMA8003550

    Draw a linear graph for the following data:


    Solution

    Solution not provided.
     

    Question 41
    CBSEENMA8003551

    Plot the points on a graph: A(4, 9): B(6, 0); C(7, 7); D(2, 4).

    Solution

    Solution not provided.
     

    Question 42
    CBSEENMA8003552
    Question 43
    CBSEENMA8003553
    Question 45
    CBSEENMA8003555

    Look at the graph of a rectangle in the figure. What are the coordinates of its vertices?



    Solution

    Solution not provided.
    Ans. A(2, 4), B(2, 2), C(7, 2), D(7, 4)

    Question 48
    CBSEENMA8003558

    A line graph is called as:
    • bar graph
    • linear graph
    • pie graph

    Solution

    B.

    linear graph
    Question 49
    CBSEENMA8003559
    Question 50
    CBSEENMA8003560
    Question 51
    CBSEENMA8003561

    The coordinates of origin are
    • (0, 0)
    • (1, 0)
    • (0, 1)

    Solution

    A.

    (0, 0)
    Question 52
    CBSEENMA8003562

    The points (5, 0) lies on
    • x-axis
    • y-axis
    • origin

    Solution

    A.

    x-axis
    Question 54
    CBSEENMA8003564

    The points (4, 2) is nearer to
    • origin
    • x-axis 
    • y-axis

    Solution

    B.

    x-axis 
    Question 55
    CBSEENMA8003565

    The points (4, 4) is
    • nearer to x-axis
    • nearer to y-axis
    • equidistance from x-axis and y-axis

    Solution

    C.

    equidistance from x-axis and y-axis
    Question 56
    CBSEENMA8003566

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