A hollow cylinder of thickness 0.7 cm and height 15 cm is made of iron. If inner radius of cylinder is 3.5 cm, then what is the total surface area (in cm2) of the hollow cylinder?
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. 759.88
inner radius, r2 = 3.5 cm. and outer radius, r1 = (0.7 + 3.5) cm = 4.2 cm.
Later surface area = 2πh (r1 + r2).
Total surface area = 2πh (r1 + r2) + 2π 
= 2 × 15 (3.5 + 4.2) + 2 × (4.22 − 3.52).
= 726 + 33.88
= 759.88 cm.
C is correct choice.
Short Trick:
In this question answer will be multiple of 11. So check the option which will be divisible by 11.
Only option 3 is divisible by 11.