A matchbox is 5cm by 8cm by 2cm. A carton is 20 cm by 40 cm by 20 cm

The carton is completely filled with matchboxes.

Work out the number of matchboxes in the carton

First, we need to check whether the carton can be fully filled. Every side can be totally divided by the side of match box. So the total volume of carton divide the volume of matchbox is the answer. 20*40*20 / (5*8*2) = 200.