A box contains 15 green and 10 yellow balls. If 10 balls are randomly drawn, one-by-one, with replacement, then the variance of the number of green balls drawn is?

We can see that the Probability of getting a green ball is = Favourable Events / Total Number of balls = 15/25
Similarly, probability of getting a Yellow ball = 10/25
Let p = 15/25 and q = 10/25
As it follows binomial distribution, n = 10
Variance = npq = 10 × 15/25 × 10/25 = 125