A rectangle has an area of 48 square centimetres and a width of 6 centimetres. Enter the number of centimetres in its length.

Explication

Since area is length multiplied by width, the missing length is 48 divided by 6. Subtracting instead gives 42 and treats the area as though it had been built by adding the two measurements, yet a shape 42 by 6 would cover far more ground.