Given,

An experiment has 10 equally likely outcomes,

Let B have n no of outcomes,

So, $$P(B) = {n \over {10}}$$

$$P(A) = {4 \over {10}}$$

$$P(A \cap B) = {4 \over {10}} \times {n \over {10}} = {{{{2n} \over 5}} \over {10}}$$

Since, A and B are independent

n is an integer

n = 5 or 10