Question

7 pens and 5 pencils together cost rs 50 whereas 7 penci and 5 pens cost rs 46 from the linear equation for the given conditions

Answer 1

let pen be x and pencil be y
according to 1st condition,
7x + 5y =50. .........(1)

according to 2nd condition,
5x + 7y = 46. .........(2)

add (1) and (2)
7x + 5y = 50
5x + 7y = 46

12x + 12y = 96
divide by 12
x + y = 8. .........(3)

sub (1) and (2)
7x + 5y = 50
5x + 7y = 46
- - -
2x - 2y = 4
divide by 2
x - y = 2. ......(4)

add (3) and (4)
x + y = 8
x - y = 2

2x =10
x. = 5

substitute x = 5 in (4)
x - y = 2
5 - y = 2
- y = 2 - 5
- y = - 3
y = 3

cost of one pen is RS 5 and cost of one pencil is RS 3