The price of wheat flour rises by 100%. By what percentage must a family reduce its consumption so that its spending on wheat flour stays the same?

💡 Solution & Explanation

Spending = price × quantity. Take the old price as 100 and the old quantity as 100, so the spending is 10,000. The new price is 200, so the quantity must become 10,000 ÷ 200 = 50. That is a cut of 50%. Shortcut: reduction % = rise ÷ (100 + rise) × 100 = 100 ÷ 200 × 100. Cutting by 100% would leave the family spending less than before.