Question

Joe opened a book store. On the first three days he sold 15, 18, and 16 books (he initially hoped he sell 17 books everyday). How many books does he need to sell on the next day to have a mean sale of 17?

Answer 1

$\frac{15 + 18 + 16 + x}{4} = 17 \\ \frac{49 + x}{4} = 17 \\ 49 + x = 17 \times4 \\ 49 + x = 68 \\ x = 68 - 49 \\ x = 19$
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