Answer : 4. "13.04%"
Explanation :

To solve this problem, let's denote:

• Initial price of sugar = P
• Initial quantity consumed = Q
• Initial expenditure = PQ

After the price increases by 15%, the new price becomes 1.15P.

To keep the expenditure constant, the new quantity consumed (let's call it Q') can be calculated using the formula:

New expenditure = New price × New quantity

Setting the new expenditure equal to the initial expenditure:

PQ = (1.15P) * Q'

Now, solve for Q':

Q' = PQ / (1.15P)

Simplify:

Q' = Q / 1.15

Now, let's find the percentage decrease in consumption:

Percentage decrease = [(Q - Q') / Q] * 100

Substituting the value of Q':

Percentage decrease = [(Q - (Q / 1.15)) / Q] * 100

Percentage decrease = [(Q * (1 - 1/1.15)) / Q] * 100

Percentage decrease ≈ [(1 - 0.8696) * 100] ≈ 13.04%

Therefore, the consumption of sugar should be decreased by approximately 13.04% to keep the expenditure on the purchase of sugar the same after a 15% increase in price.