i am amaan shaikh i am study in class 8 in ambika public school

Let P be the marked price,

then the cost to Raju was (0.8)P, which represents a 20% discount.

When Raju sold the watch, his profit was P - .8P = 0.2 P

The percent gain for Raju = (Profit/Cost)* 100 = (.2p/.8P)*100 = 25%

Plug in some numbers to make sure this makes sense:

If the marked price is $100, Raju spends $80. He sells it for $100, so he makes $20 on his $80 investment, and $20 is 25% of $80, so this answer makes sense.