This question was a simple question on probability.  From the information given, candidates were expected to obtain the complimentary probabilities i.e. if P(m) = 0.9, then P(m1) = 1 - 0.9 = 0.1 similarly, P(Phy1) = 1- 0.75 = 0.25 and (Bio1) = 1 - 0.8 = 0.2.  The required probability was          P(m and Phy and Bio1) or P(m and phy1 and bio) or P(m1 and phy and bio) or P(m and phy and bio) = (0.9 x 0.75 x 0.2)+(0.9 x 0.25 x 0.8) + (0.1 x 0.75 x 0.8) + (0.9 x 0.75 x 0.8) = 0.915.
 A good number of the candidates were reported to have obtained this result. However, some candidates did not, either by not obtaining the complimentary probabilities or by not including the probability of scoring high in the three subjects.