CBSE Class 10-Mathematics: Chapter –3 Pair of Linear Equation in Two Variables Part 13
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Question 2:
Form the pair of linear equations in the following problems and find their solutions graphically.
(i) 10 students of class X took part in a mathematics quiz. If the number of girls is 4 more than the number of boys, find the number of boys and girls who took part in the quiz.
(ii) 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.
Answer:
(i) Let number of boys who took part in the quiz
Let number of girls who took part in the quiz
According to given conditions, we have
And
For equation , we have following points which lie on the line
For equation , we have following points which lie on the line
We plot the points for both of the equations to find the solution.

Find Their Solutions Graphically
We can clearly see that the intersection point of two lines is
Therefore, number of boys who took park in the quiz and, number of girls who took part in the quiz =.
(ii) Let cost of one pencil Rs and Let cost of one pen Rs
According to given conditions, we have
(1)
(2)
For equation , we have following points which lie on the line
For equation , we have following points which lie on the line

Find Their Solutions Graphically
We can clearly see that the intersection point of two lines is .
Therefore, cost of pencil = Rs 3 and, cost of pen