The ratio of a quarterback's completed passes to attempted passes is 6 to 7. If he attempted 21 passes, find how many passes he completed.

The ratio of completed passes to attempted passes is 6:7, so completed passes are 6/7 of the attempts. With 21 attempts, 21 ÷ 7 = 3, and 3 × 6 = 18 completed passes. The correct choice is 18 passes.

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