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The neighbor’s dog barks at a squirrel every 15 minutes at night. If he first barks at 10 p.m., when you’re trying to fall asleep, how many times will he bark by 2 a.m., when you give up trying to sleep and decide to read a book instead?

A 17 times

The time between 10 p.m. and 2 a.m. is 4 hours or 240 minutes. Divide the total number of minutes in the time period by 15 minutes — the interval that the dog barks. Then add 1 because the dog started barking at the beginning of the period: (240 ÷ 15) + 1 = 17.