A square sheet of card has side cm. A square of side cm is cut from each corner and the sides are folded up to make an open box. What is the greatest possible volume of the box, in cm?

Answer and explanation

Correct answer: E.

  1. Step 1: The base is a square of side and the height is , so .
  2. Step 2: . In the allowed range the relevant stationary point is .
  3. Step 3: at , so it is a maximum, and .
Answer
.
Why not the others: gives , gives , and gives , all below ; is , the area of the sheet; and are not the value of at the stationary point.

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