# NCERT Exemplar Solutions Class 10 Mathematics Solutions for Surface Areas and Volumes - Exercise 12.4 in Chapter 12 - Surface Areas and Volumes

Question 12 Surface Areas and Volumes - Exercise 12.4

A heap of rice is in the form of a cone of diameter 9 m and height 3.5 m. How much canvas cloth is required to just cover the heap?

According to the question,

Consider conical heap,

Base Diameter = 9 cm

So, base radius, r = 4.5 cm

Height, h = 3.5 cm

We know that,

Slant height,

l=\sqrt{r^{2}+h^{2}} \\ \Rightarrow l=\sqrt{(4.5)^{2}+(3.5)^{2}}=\sqrt{20.25+12.25} \\ \Rightarrow l=\sqrt{32.5}=5.7 \mathrm{~cm}

We also know that,

Canvas requires to just cover heap = Curved surface area of conical heap

And curved surface area of a cone = πrl

Therefore, the canvas required = π(4.5)(5.7) = 80.61 cm2

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