While Eddie is away on holidays his swimming pool has a leak. Each day it loses half the water still in the pool. Normally, it’s 1.6 metres deep, but when Eddie gets home there is only 10 centimetres of water in the bottom. How long has the pool been leaking?
Work back from 10 centimetres, doubling the amount each day, until you get to 160 centimetres.
One day before Eddie got home, the pool had 2 x 10 = 20 centimetres.
Two days before he got home it was 2 x 20 = 40 centimetres.
Three days before he got home it was 2 x 40 = 80 centimetres.
Four days before he got home it was 2 x 80 = 160 centimetres – it was full!
The pool was leaking for 4 days.