Calculate the number of combinations, given n = 10 and r = 4. 210 330 495 1,680
Question
Calculate the number of combinations, given n = 10 and r = 4.
Choices:
- 210
- 330
- 495
- 1,680
Solution
To calculate the number of combinations, we use the formula for combinations which is C(n, r) = n! / [r!(n-r)!], where "n" is the total number of items, "r" is the number of items to choose, and "!" denotes factorial.
Step 1: Calculate n! 10! = 10 × 9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1 = 3,628,800
Step 2: Calculate r! 4! = 4 × 3 × 2 × 1 = 24
Step 3: Calculate (n-r)! (10-4)! = 6! = 6 × 5 × 4 × 3 × 2 × 1 = 720
Step 4: Substitute these values into the formula C(10, 4) = 3,628,800 / (24 × 720) = 210
So, the number of combinations of 10 items taken 4 at a time is 210.
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