x + y = 21
x + y - 8 = 3*y + 5
Subtract y from both sides.
x - 8 = 3y - y + 5
x - 8 = 2y + 5 Substitute x = 21 - y into the equation
21 - y - 8= 2y + 5
13 = 3y + 5 Subtract 5 from both sides
13 - 5 = 3y
8 = 3y Divide by 3
y = 8/3
x + y = 21
x + 8/3 = 21
x = 21 - 8/3
x = 18 1/3 or 18.333333
Check
The smaller number is 8/3
x + y - 8 = 3*(8/3) + 5 Remember that x + y = 21
21 - 8 = 8 + 5
13 = 13 and they check. Which one is the smaller number does not become a factor until you check your answer.
