For Mrs Rekha, probability of having a baby of BW < 2500 gms is 0.50 and of having a BW 2500-2999 gms is 0.20. So the probability for Mrs. Rekha to have a baby of BW < 3 kg is

Here, for Mrs Rekha, probability of having a baby of BW < 2500 gms, P(A) is 0.50 and of having a BW 2500-2999 gms, P(B) is 0.20 Thus, the probability for Mrs. Rekha to have a baby of BW < 3 kg is P(Total) = P(A) + P(B) = 0.50 + 0.20 = 0.70 (70%) There is one more possibility, i.e. probability of having a baby of BW > 3 kg, whose probability P(C) will be 1 – (P(A) + P(B)) = 0.30 (30%).