Percentage change
A standard method from Variations: the steps and worked examples.
Steps
Write each new value as a factor (+20% → 1.2), put the factors into the equation, and compare with 1. No need to find k.
Worked examples
Example 1: In example 1, x increases by 20% and z decreases by 10%. Find the percentage change in y.
new y = k(1.2x)² / (0.9z) = (1.44 / 0.9) × kx²/z = 1.6y
y increases by 60%For the whole topic, read Variations: key points, common mistakes and how the DSE tests it.