Question
5 pencils and 7 pens together cost Rs. 50, whereas 7 pencils and 5 pens together cost Rs. 46. Find the cost of one pencil and that of one pen.
Solution
Let cost of 1 pencil be Rs. ,v and cost of 1 pen be Rs. y
Case I. Cost of 5 pencils = 5x
Cost of 7 pens = 7y
<>According to question,
5x + 7y = 50
Case II. Cost of 7 pencils = 7x
Cost of 5 pens = 5y
According to question,
7x + 5y = 46
Thus, we have
Thus, we have following table :
Fig. 3.5.
When we plot the graph of the given equation, we find that both the lines intersect at the point (3, 5). So, x = 3,y = 5 is the required solution of the pair of linear equation.
Hence, the cost of 1 pencil be Rs. 3 cost of 1 pen be Rs. 5.
