If n P r -840- n C r -35- then n is equal toA- 1B- 3C- 5D- 7

The correct option is D 7 ^nP_r/^nC_r = 24 ⇒ r! = 24 ⇒ r = 4 ∴^nC_4 = 35 ⇒ n = 7 ...

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Binomial Coefficients

If n P r =840...

Question

If $^{n} P_{r}$ = 840, $^{n} C_{r}$ = 35, then n is equal to

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^{n} P_{r} = 840,^{n} C_{r} = 35

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^{n} P_{r} = 840,^{n} C_{r} = 35

n \sum r = 0 {\frac{^{n} C_{r - 1}}{^{n} C_{r} +^{n} C_{r - 1}}}^{3} = \frac{25}{24}

If $^{n} C_{r}$ = $^{n} C_{r - 1}$ and $^{n} P_{r}$ = $^{n} P_{r + 1}$ , then the value of n is

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