Explanation:

Let the number of 50 paise, one rupee and two rupee coins in the bag be x, y and z respectively.

There are 80 coins with a total amount of Rs. 90.

x + y + z = 80 ……… (i)

0.5x + y + 2z = 90 ………. (ii)

The number of 50 paise coins and two rupee coins together is equal to the number of one rupee coins.

x + z = y ………..(iii)

From (i) and (iii), y = 40

Substituting this in (i) and (ii) and solving this in (i) and (ii) and solving, z = 20 and x = 20

Hence, the number of two rupee coins in the bag is 20.

Hence, Option B