The tip
When a cost has a one-time fee plus a monthly charge, it is a line. Use two data points to find the slope (the monthly charge), then plug one point back in to find the starting fee.
Try it
A gym charges a one-time sign-up fee plus a fixed monthly fee. The total cost for 3 months is $110, and the total cost for 7 months is $210. What is the one-time sign-up fee?
- A$25
- B$35
- C$40
- D$60
Reveal answer
Answer: B. $35
The monthly fee is (210 - 110) / (7 - 3) = 100 / 4 = $25. For 3 months: fee + 3(25) = 110, so the fee is 110 - 75 = $35. Check: 35 + 7(25) = 210.
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