WAEC - Further Mathematics (2010 - No. 22)
The probabilities that a husband and wife will be alive in 15 years time are m and n respectively. Find the probability that only one of them will be alive at that time.
mn
m + n
m + n - 2mn
1 - mn
Forklaring
P(only one alive) = P(husband and not wife) + P(wife and not husband)
= m (1 - n) + n ( 1 - m)
= m - mn + n - mn
= m + n - 2mn