Question

If 3x + 7y = 12 and x-y= 1, then what is the value of 5x + 5y?

Answer 1

14.

Explanation:

3x + 7y = 12

x - y = 1 Multiply this by -3:

-3x + 3y = -3 Add this to equation 1:

0 + 10y = 9

so y = 9/10 = 0.9.

x - 0.9 = 1

x = 1.9.

So 5x + 5y = 5*1.9 + 5*0.9

= 14.