Question : The radius of the base of a conical tent is 8 m and its height is 15 m, what is the cost of the material needed to make it if it costs Rs. 54 per $\pi\ \mathrm{m}^2$?
Option 1: INR 6454
Option 2: INR 7344
Option 3: INR 8678
Option 4: INR 7454
Correct Answer: INR 7344
Solution :
The radius of the base of a conical tent, $r$ = 8 m
Height, $h$ = 15 m
$\therefore$ Slant height, $l$ = $\sqrt{r^2 + h^2}=\sqrt{8^2 + 15^2}=\sqrt{289}= 17$ m
Curved surface area of cone = $\pi rl=8 × 17× \pi=136\pi$ m
2
Cost per $\pi$ m
2
= INR 54
$\therefore$ Total cost = 136 × 54 = 7344
Hence, the correct answer is INR 7344.
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