The neighbor’s dog barks at a raccoon 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 have barked by 2 a.m., when you give up trying to sleep and decide to read a book instead?
The dog is barking every 15 minutes, or 4 times per hour.
The time between 10 p.m. and 2 a.m. is 4 hours.
Multiply the total number of hours in the time period by 4 barks per hour.
Then add 1 because the dog barked at the beginning of the period also:
(4 × 4) + 1
= 16 + 1
= 17.