By what per cent does the curved surface area of a cylinder decrease, if the radius is increased by 10% and the height is decreased by 40% ?

Correct option is B

Given:

Radius is increased by $10\%\; =X=\; +10$

Height is decreased by $40\%\; =Y\; =\; -40$

Formula Used :   

Using successive percentage: 

Net percentage change: 

 = ​$$(X+Y+\frac{XY}{100})$$% 

Solution:  

Using the value and formula;

= 10 + (- 40 ) + $$(\frac{-400}{100})$$%

 =  - 30 - 4 = - 34%

The curved surface area of a cylinder is decreases by 34%.​

The correct answer is option ( b ) 34