In how many ways can 3 distinct numbers be chosen from the set such that the sum of the numbers is odd?
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If the sum of three integers is odd, then two cases are possible:
To pick three distinct odd numbers from the given set, there are ( 3 5 ) = 2 ! × 3 ! 5 ! = 1 0 ways.
To pick two even and one odd number from the set, there are ( 2 5 ) × ( 1 5 ) = 5 0 ways.
Therefore, the three numbers can be chosen in 1 0 + 5 0 = 6 0 ways. □