A vending machine sells chips at $0.55 and candy at $0.75. Last month the vending machine yielded at $189.00 with the sale of 280 items. How many packages of chip were purchased last month?

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