WAEC 2019 · Paper 2 · Q5
A fair die with faces 1, 2, 3, 4, 5 and 6 is tossed twice. Calculate the probability that the sum of the numbers that show up is:
- (a)
a multiple of 3;
- (b)
between 3 and 6.
Worked solution (try it first)
- Two throws give 36 equally likely outcomes.
(a)
- Sums that are multiples of 3: 3 (2 ways), 6 (5 ways), 9 (4 ways) and 12 (1 way): 12 outcomes, so .
(b)
- Between 3 and 6 means a sum of 4 (3 ways) or 5 (4 ways): 7 outcomes, so .