The ratio of the base area of a hollow cone to that of its curved surface is 1:4. If its base radius is 7cm, calculate the slant height of the cone
- 7cm
- 22cm
-
28cm
- 49cm
- 154cm
The correct answer is: C
Explanation
The base of a cone is a circle, r = 7cm
Base area of a cone = \(\pi\)r\(^2\)
Curve surface area of a cone = \(\pi\)l
\(\pi\)r\(^2\) : \(\pi\)l = 1 : 4
\(\frac{\pi r^2}{\pi l}\) = \(\frac{1}{4}\)
\(\frac{r}{l} = \frac{1}{4}\)
\(\frac{7}{l} = \frac{1}{4}\)
cross multiplying
l = 4 x 7 = 28cm.