Water lilies grow extremely rapidly. In one pond, a water lily grew so fast that each day it covered a surface area double that of the area it had covered the previous day. At the end of the 30th day, it had covered the pond entirely. How long do you think it will take for two such water lilies to cover the whole pond?
Solution: It will take 29 days for two water lilies to cover the whole pond.
Each water lily will need to cover half of the pond. The water lilies will cover half of the pond on the 29th day.
The bathtub filling rate is:
The cold tap will fill the bathtub at 1/18 tub/minute
The hot tap will fill the bathtub at 1/15 tub/minute
The drain will drain the bathtub at 1/10 tub/minute
The nett bathtub fill rate is: 1/18 + 1/15 – 1/10 = 1/45 tub/minute
The water will fill 1/45 of the tub in 1 minute, so the tub will be full in 45 minutes.