Subject: General Aptitude · Chapter: Volume and Surface Area · Exam: · Marks: · Difficulty:
Area of the canvas cloth needed to erect a right conical tent of height 12 ft and circular base having circumference $10 \pi \mathrm{ft}$ is
(a)60 sq ft
(b)65 sq ft
(c)$65 \pi \mathrm{sq}$ ft
(d)$120 \pi \mathrm{sq} \mathrm{ft}$
Answer
Answer (as printed): C
Explanation
Let the radius of base be $r \mathrm{ft}$. Then, $2 \pi r=10 \pi$ or $r=5$. $$l=\sqrt{r^{2}+h^{2}}=\sqrt{5^{2}+(12)^{2}}=\sqrt{169}=13 \mathrm{ft} . \text { ∴ Area of cloth }=\pi r l=(\pi \times 5 \times 13) \mathrm{sq} \mathrm{ft}=65 \pi \mathrm{sq} \mathrm{ft} \text {. }$$
Explanation as extracted from the printed page; notation may be imperfect.