Question

Find two numbers such that the sum of thrice the first and the second is 142, and four times the first exceeds the second by 138. how does it become 4x -y = 138
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Answer 1

let x,y be the two numbers

3x+y=142. (1)

4x-y=138. (2)

From (2)

y=4x-138. (3)

Substituting (3) in (1)

3x+(4x-138)=142

7x=142+138

7x=280

x=40

In (2)

y=4*40-138=160-138=22

x=40,y=22