The price of sugar goes up by 60%. By what percent must Sunita cut her consumption so that her monthly spending on sugar stays exactly the same?

Spending = price × quantity. With the price at 1.6 times its old value, the quantity must fall to 1/1.6 = 0.625 of what it was — that is, she keeps 62.5% and gives up 37.5%. (62.5 is the part she still buys, not the cut; and cutting by the same 60% the price rose by would leave her spending only $0.40\times 1.60=0.64$ of the old amount.)