A number is increased by 20% and then decreased by 25%. Find the percentage change.

Start with 100. Increase by 20%: 100 × 1.20 = 120.

Now decrease 120 by 25%: 120 × 0.75 = 90.

The number went from 100 to 90, so it is a 10% decrease. The two changes do not cancel because the 25% is taken from the bigger new value.