Let S be the set of five-digit numbers formed by the digits 1, 2, 3, 4 and 5, using each digit exactly once such that exactly two odd positions are occupied by odd digits. What is the sum of the digits in the rightmost position of the numbers in S
Correct Answer : B
Let H be a set of 2000 nonzero real numbers. How many negative elements should H have in order to maximize the number of four-elemen subsets of H with a negative product of elements?
How many zeros at the end of binary expansion of 100!?
Find the number of pairs of positive integers (a, b) such that a!+b! = ab