Question

A first number plus twice the second number is 7. Twice the first number plus the second totals 20. Find the number

Answer 1

As per the problem

A first number plus twice the second number is 7

Twice the first number plus the second totals 20

Let the first number is x and second number is y then we can write

$x+2y=7.........(i)\\ \\ 2x+y=20........(ii)\\ \\ \text{Now solve these two equations together , multiply equation 1 by 2 }\\ \text{and subtract from equation 2}\\ \\ \ \ 2x+y=20\\ -(2x+4y=14)\\ ------\\ -3y=6\\ -----\\ y=-2\\ \text{Substitute this value in equation one we get}\\ \\ x-4=7\\ \\ x=11\\ \\ \text{Hence the two numbers are }\\ x=11, y=-2$

Answer 2

X+y=7
2x+y=20

y=7-x

Now substitute

2x+7-x=20
x+7=20
x=20-7
x=13

Which means y=-6 if you put it into the first 2 equations