# Two positive integers have a sum of 9, what is the probability that one of them was 7.

*print*Print*list*Cite

### 2 Answers

Two positive integers have a sum of 9. The number of positive number pairs that add up to 9 are (8, 1), (1, 8), (7, 2), (2, 7), (3, 6), (6, 3), (4, 5), (5, 4)

There are 8 pairs that add up to 9. Of these 2 of them have the integer 7. This gives a probability of 2/8 = 0.25

**The probability that one of the two positive integers that add up to 9 being 7 is 0.25**

.25 is correct but there are only four possible combinations: 1 and 8, 3 and 6, 4 and 5. These are not dice but numbers. 5 and 4 are the same numbers as 4 and 5, etc. There is only one probability that one of the numbers would be 7. It doesn't matter which one.