Question

an open cylinder oil tank has diameter 14 m and height 9 m if the inner side of tank has to be painted all over what will it cost at rupees 40 per square metre​

Answer 1

TSA =

$2\pi {r}^{2} \: + \: 2\pi rh \\ \\ 2\pi r = (h + r) \\ \\ 2 \times \frac{22}{7} \times 7 \times 16 \\ \\ 44 \times 16 = 704 {m}^{2} \\ \\ total \: cost \: = 704 \times 40 = rs28610$

diameter was divided by 2 = 14/2 =7

and then height added = (r +h) (7+9)=16

answer = rs28610