# GMAT Official Study Guide – PS #17 (Level: 300-400)

**Problem**:

A bakery opened yesterday with its daily supply of 40 dozen rolls. Half of the rolls were sold by noon, and 80 percent of the remaining rolls were sold between noon and closing time. How many dozen rolls had not been sold when the bakery closed yesterday?

**Solution**:

If half of the rolls were sold by noon, ⅟₂*40 dozen = 20 dozen rolls were sold by noon and 20 dozen rolls remained.

80%, or 0.8 of the remaing rolls = .8*20 dozen = 16 dozen were sold by closing.

Thus, there were 20 dozen – 16 dozen = 4 dozen rolls remaining at closing.

**Strategy**:

Percents can be written as fractions or decimals. When working with percents, the word “OF” means to multiple. In this problem, half of 40 dozen translates to ⅟₂*40 dozen = 20 dozen. Also, 80% of 20 dozen translates to .8*20 dozen = 16 dozen.

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