A person loses Rs. 20 by selling some bananas at the rate of Rs. 3 per banana and gains Rs.30, if he sells them at Rs. 3.25 per banana. The number of bananas sold by him?

Go through options. Consider option (b)
200 x 3.25 - 200 x 3 = Rs. 50 = ( 30+20 )
Hence option, (b) is correct
Alternatively: Rs. 0.25 is the difference on 1 banana
Rs. 1 is the difference on 1/0.25 = 4 bananas
Rs. 50 is the difference on 4 x 50 = 200 bananas