9. The Caterpillar's Ascent. The height of the pole is 20 meters. The caterpillar crawls up it, during the day it climbs 5 meters, and at night it slides down 4 meters. How long will it take for the caterpillar to reach the top of the pole?
9. The usual answer: in 20 days, but... Since the caterpillar climbs 1 meter per day, therefore, in 15 days it will climb 15 meters, and on the sixteenth day it will climb another 5 meters and reach the top of the pole...

![](https://cdn.mathpix.com/cropped/2024_05_21_b6bdef2bf90cccc464adg-009.jpg?height=286&width=1085&top_left_y=548&top_left_x=494)