Cross-multiplication is a procedure for calculating direct and inverse proportionality.
Direct proportionality – “the more, the more:” 1 brick weighs 5 kg, how much do 150 bricks weight?
Inverse proportionality – “the more, the less:” If the car is driven at an average speed of 90 km/h, it will take 40 minutes. How long does it take for an average speed of 130 km/h?
