Suresh saves 20% of his monthly income. Next year his income goes up by 25% while his monthly spending goes up by 20%. What happens to his monthly savings?

Take his income as 100: he saves 20 and spends 80. Next year income = 125 and spending = $80\times 1.20=96$, so savings = 125 - 96 = 29. The change is $(29-20)/20=9/20=45$%. 'A rise of 5%' subtracts the two given rates (25 - 20), which is meaningless here since they act on very different amounts. 'A rise of 9%' reads the gain of 9 units as a percentage, and 'a rise of 25%' just repeats the income rise. Savings swing hardest because they start from the smallest base.