Count the possible combinations of 2 numbers chosen from the list 99 98 97 96 95 94 93 92 91

The number of ways to choose r objects out of n objects is:

C (n, r) = (n!) / (r! * (n-r) !)

The number of ways to choose 2 numbers out of a list of 9 numbers is:

C (9,2) = 9! / (2! * 7!)

= 9*8 / 2!

= 9*8/2

= 36

Here are all the possible combinations:

98 97

98 91

98 93

98 99

98 96

98 94

98 92

98 95

97 91

97 93

97 99

97 96

97 94

97 92

97 95

91 93

91 99

91 96

91 94

91 92

91 95

93 99

93 96

93 94

93 92

93 95

99 96

99 94

99 92

99 95

96 94

96 92

96 95

94 92

94 95

92 95