The probability of winning the first game by India is 1/3. Say, it is P(A) = 1/3. Similarly, the probabilities of winning the second and the third game are P(B) = 1/3 and P(C) = 1/3 respectively. We have, from the theory of joint probability-
Probability of winning all three matches by India = P(ABC) = P(A and B and C) = P(A) * P(B) * P(C) = 1/3 * 1/3 * 1/3 = 1/27.