Multiple choice

The curved surface area of a frustum is 660 cm2. If the slant height and one of the base radii are 21 cm and 3 cm, respectively, find the other radius.

  1. 13 cm

  2. 10 cm

  3. 7 cm

  4. 49 cm
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Curved surface area of a frustum = pi * (r1 + r2) * l. 660 = (22/7) * (3 + r2) * 21. 660 = 22 * 3 * (3 + r2). 660 = 66 * (3 + r2). 10 = 3 + r2. r2 = 7.

AI explanation

Using the curved surface area of a frustum formula, pi times the sum of the radii times the slant height equals the lateral surface area. Substituting the given values gives pi times (3 plus the other radius) times 21 equals 660. Dividing 660 by 21 pi gives the sum of the two radii as 10. Subtracting the known radius of 3 from 10 gives the other radius as 7 cm.

Keep practicing — related questions