Question

x+y =7and 5x+2y=7by cross multiple

Answer 1

let it be in proportion
then,x+y
$x + y \div 5x + 2y = 7 \div 7 \\ 7 \times x + y = 7 \times 5x + 2y \\ 7x + 7y = 35x + 14y \\ 7x - 35x = 14y - 7y \\ - 28x = 7y \\ xy = - 28 \div 7 = - 4$
hope it helps

Answer 2

2(x+y)=2×7
2x+2y = 14______1

5x+2y = 7_______2

now eq2nd - eq1st

then

3x = -7
X = -7/3

putting the value of X

then..

5x+2y = 7
5(-7/3) + 2y = 7
2y = 7+35/3
2y = 56
y = 56/2 = 28

your answer is "X=-7/3" and "Y=28"

hope it will help you.