Multiple choice

The surface area of a cylindrical box is $\displaystyle 132\ { mm }^{ 2 }$ and its height is $4 $mm. Find its radius.

  1. $\displaystyle 2 $ ${ mm }$
  2. $\displaystyle 3 $ ${ mm }$
  3. $\displaystyle 4 $ ${ mm }$
  4. $\displaystyle 5 $ ${ mm }$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Surface area of a cylinder = 2 * pi * r * (r + h). 132 = 2 * (22/7) * r * (r + 4). 132 * 7 / 44 = r(r+4) => 21 = r^2 + 4r => r^2 + 4r - 21 = 0. (r+7)(r-3) = 0. Since radius must be positive, r = 3.

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