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Arithmetic Progressions
Question
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The sum of the 4th and 8th terms of an A.P. is 24 and the sum of the 6th and 10th terms is 44. Find the first three terms of the A.P.

Answer

Case I.
T4 + T8 = 24
⇒ a + (4 – 1)d + a + (8 – 1)d = 24
⇒ a + 3d + a + 7d = 24
⇒ 2a + 10d = 24
⇒ a + 5d = 12 ...(i)
Case II. T6 + T10 = 44
⇒ a + (6 – 1)d + a + (10 – 1)d = 44
⇒ a + 5d + a + 9d = 44
2a + 14d = 44
⇒ a + 7d = 22 ...(ii)
Subtracting (i) from (ii), we get
(a + 7d) – (a + 5d) = 22 – 12
⇒ a + 7d – a – 5d = 10
⇒ 2d = 10
⇒ d = 5

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Some More Questions From Arithmetic Progressions Chapter

In which of the following situational, does the list of numbers involved make an arithmetic progression, and why?

The cost of digging a well for the first metre is Rs. 150 and rises by Rs. 50 for each succeeding metre.

Write first four terms of the AP, when the first term a and the common difference d are given as follows:
a – 10, d = 10

Write first four terms of the AP, when the first term a and the common difference d are given as follows:
a = –2, d = 0

Write first four terms of the AP, when the first term a and the common difference d are given as follows:
a = 4, d = – 3

Write first four terms of the AP, when the first term a and the common difference d are given as follows:

a = – 1.25, d = – 0.25

For the following APs, write the first term and the common difference
3, 1, – 1, – 3, . . .

For the following APs, write the first term and the common difference
– 5, – 1, 3, 7, . . .