Multiple choice

If the radius of a cylinder increases by $y$ cm, its volume becomes $V$ $\displaystyle cm^{3}$ . If its height increased by $4y$ cm, its volume would become $V$ $\displaystyle cm^{3}$. If its radius as well as its height equals $6$ cm, then find $y$.

  1. $10$
  2. $12$
  3. $14$
  4. $16$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Original volume V = pi * r^2 * h. New volume 1: pi * (r+y)^2 * h = V. New volume 2: pi * r^2 * (h+4y) = V. Given r=6, h=6, we have (6+y)^2 * 6 = 6^2 * (6+4y). Solving (6+y)^2 = 6(6+4y) leads to 36 + 12y + y^2 = 36 + 24y, so y^2 = 12y, y = 12.

AI explanation

The initial radius and height are both 6 cm, making the original volume V equal to 216(pi). The first condition states V = (pi)(6 + y)^2 times 6, meaning 216 = 6 times (6 + y)^2, which simplifies to (6 + y)^2 = 36. Solving this equation gives a y value of 12, and this is confirmed by the second condition where 216(pi) equals (pi)(6^2) times (6 + 4y), leading to the exact same result. The value of y is 12.