A cable is sold at a constant price per metre. Nine metres cost $22.50. How many metres can be bought for$40.00?

Explanation

The unit price is $22.50 divided by 9, or$2.50 per metre, and $40.00 divided by$2.50 gives 16 metres. A result of 17.5 metres comes from adding the price difference to the length, which does not preserve the constant price per metre.