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

2 Answers | Add Yours

justaguide's profile pic

justaguide | College Teacher | (Level 2) Distinguished Educator

Posted on

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

billdelaney's profile pic

William Delaney | (Level 2) Distinguished Educator

Posted on

.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.

We’ve answered 333,950 questions. We can answer yours, too.

Ask a question