The amount of concrete, c, needed to make a walkway around a circular swimming pool varies directly as the square of the diameter, d, of the
pool. Which statement is true?
OA If the diameter of the pool is doubled, the amount of concrete needed is multiplied by 2.
•B. If the diameter of the pool is doubled, the amount of concrete needed is multiplied by 4.
OC. If the diameter of the pool is halved, the amount of concrete needed is multiplied by 2.
OD. If the diameter of the pool is halved, the amount of concrete needed is multiplied by 4.

The amount of concrete needed after doubling the diameter of the circle will be multiplied by 4 by the initial amount. Hence, the correct option is (B).

What are direct proportions?

Direct proportions are the proportions where a variable changes with another variable by direct mean so the coefficient of constant will be direct.

For example y ∝ x² here y varies with respect to x square.

y = Kx² where k will be the coefficient of constant.

Given that amount is Amount ∝ d²

Amount = k d²

By doubling the diameter

Amount = k (2d)²

Amount = 4 kd²

Amount = 4 × initial amount hence, the amount will be multiplied by 4.

For more information about proportions relations?

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