20 Combinations of 2
•
•
2 min read
Evaluate the combination:
20C2
A unique order or arrangement
| nCr = | n! |
| r!(n - r)! |
where n is the number of items
r is the unique arrangements.
| 20C2 2 | 20! |
| 2!(20 - 2)! |
n! = n * (n - 1) * (n - 2) * .... * 2 * 1
n! = 20!
20! = 20 x 19 x 18 x 17 x 16 x 15 x 14 x 13 x 12 x 11 x 10 x 9 x 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1
20! = 2,432,902,008,176,640,000
(n - r)! = (20 - 2)!
(20 - 2)! = 18!
18! = 18 x 17 x 16 x 15 x 14 x 13 x 12 x 11 x 10 x 9 x 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1
18! = 6,402,373,705,728,000
r! = 2!
2! = 2 x 1
2! = 2
| 20C2 = | 2,432,902,008,176,640,000 |
| 2 x 6,402,373,705,728,000 |
| 20C2 = | 2,432,902,008,176,640,000 |
| 12,804,747,411,456,000 |
20C2 = 190
