Multiple choice

Oliver bought x number of gifts, each having the same price. If he now adds a gift costing \$39, the average cost increases by \$2, but if he adds a gift costing \$15, then the average cost decreases by \$1. How many gifts did he buy initially?

  1. 5

  2. 6

  3. 7

  4. 8

  5. 9
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let S be sum of prices and n be number of gifts. S/n = A. (S+39)/(n+1) = A+2. (S+15)/(n+1) = A-1. Subtracting: 24/(n+1) = 3. n+1 = 8, so n = 7.

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