On any day, the probability that a boy eats his prepared lunch is 0: 5 . the probability that his sister eats her lunch is 0: 6 . the probability that the girl eats her lunch given that the boy eats his is 0: 9 . determine the probability that:

Y it is right. Apparently the answer to a) is 920
9
20
because since the boy ate his lunch, the girls probability of eating is 0.9 and if you multiply the two probabilities you get 920
9
20
. However this does not seem to take into account the possibility that the girl ate her lunch first, in which case the probability of both eating is 310
3
10
.