Expert: Scott A Wilson - 10/7/2009

Question
x +  9y = 88
2x + 8y = 86

practice problem and i cannot get it

Answer
Given x +  9y = 88 and 2x + 8y = 86, the first one can have 9y subtracted from both sides,
giving x = 88 - 9y.

This can be put in the second equation, giving 2(88-9y) + 8y = 86.

Multiplying it out gives 176 - 18y + 8y = 86.
Combining the y's gives 176 - 10y = 86.
Adding 10y - 86 to both sides gives 90 = 10y, or y = 9.

The 1st equations says the x + 9y = 88, so x + 81 = 88, so x = 7.
Checking the 2nd equation gives 2(7) + 8(9) = 14 + 72 = 86, so this checks,
and the answer x=7, y=9 is correct.