question_answer

The height of a conical tank is 60 cm and the diameter of its base is 64 cm. The cost of painting it from outside at the rate of Rs. 35 per sq m is                                   

A)  Rs. 52.00 (approx)        

B)  Rs. 39.20 (approx)                                 

C)  Rs. 35.20 (approx)

D)  Rs. 23.94 (approx) 

Correct Answer: D

Solution :

\[H=60\,cm\] \[R=32\,cm=\]Radius Area of the curved surface \[=\pi RL\]             \[L=\sqrt{{{R}^{2}}+{{H}^{2}}}\]             \[=\sqrt{{{(32)}^{2}}+{{(60)}^{2}}}\] \[\therefore \]      \[L=\sqrt{1024+3600}\]             \[=4624=68\,cm\] Area of the curved surface \[=\pi RL=\frac{22}{7}\times 32\times 68\] \[\therefore \] Total cost of painting             \[=35\times \frac{22}{7}\times 32\times 68\times \frac{1}{1000}\] \[(100\,cm=1\,m)\]                         \[=5\times 22\times 32\times 68\times \frac{1}{1000}\]                         \[=(100\,cm=1\,m)\]                         \[=23.94\] approx.