X = chips, y = candy
0.55x + 0.75y = 189
x + y = 280
Solve the system of equations by eliminating one variable.
0.55x + 0.75y = 189
0.55x + 0.55y = 154
Multiply the whole second equation by 0.55 so both x's in both equations have the same value. Then subtract the second equation from the first so you're left with:
0.2y = 35
y = 175
Sub this y-value back into either equation to get x.
x + 175 = 280
x = 105
So 105 bags of chips were purchased
