NECO 2005 Mathematics · Question 9
Two fair dice are tossed together once. What is the probability of getting a total of at least 9 from the outcome?
Options
- A.
- B.
- C.
- D.
- E.
Answer: C.
Explanation written with AI and checked against the answer key
Analyze the question: Two fair dice are tossed, and we want P(sum ≥ 9). The total number of outcomes is 6 × 6 = 36.
Concept: Probability = (favourable outcomes) ÷ (total outcomes). Count the ways to get each total from 9 to 12.
Solution:
- Sum = 9: (3,6), (4,5), (5,4), (6,3), which is 4 ways
- Sum = 10: (4,6), (5,5), (6,4), which is 3 ways
- Sum = 11: (5,6), (6,5), which is 2 ways
- Sum = 12: (6,6), which is 1 way
Total favourable = 4 + 3 + 2 + 1 = 10
P(sum ≥ 9) = 10/36 = 5/18
Answer: Option C, 5/18.
Tip: For dice sums, the number of ways rises by 1 up to 7 and then falls by 1. The counts for sums 2 to 12 are 1, 2, 3, 4, 5, 6, 5, 4, 3, 2, 1. For "at least 9", add the last four: 4+3+2+1 = 10. Always simplify the fraction over 36.
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