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If nP_{r} = 720(nC_{r}), then r is equal to:

#### Options

4

5

6

7

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#### Solution

**6**

**Explanation:**

Given nP_{r} = 720(nC_{r})

`(n!)/((n-r)!) = 720 (n!)/(r!(n-r)!)`

1 = `720/(r!)`

r! = 720

r! = 6 × 5 × 4 × 3 × 2 × 1

r! = 6!

r = 6

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