# C (7,2) = ? This is a problem on a number sense test that I don't understand what it is asking. The answer is 21. What type of problem is this and how is it solved?

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Expert Answers

justaguide | Certified Educator

C(7,2) is represents the number of ways of choosing 2 elements from a set that has 7 elements.

The general formula for `C(n r) = (n!)/(r!(n - r)!)`

`C(7, 2) = (7!)/(2!(7-2)!)`

=> `(7!)/(2!*5!)`

=> `(7*6)/2 `

=> 7*3

=> 21

**The value of C(7, 2) = 21**