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If 20Cr=^20C(r+4), then rC3 is equal to:...

If `20C_r=^20C_(r+4)`, then `rC_3` is equal to:

A

50

B

56

C

66

D

None of these

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JBD PUBLICATION-PERMUTATIONS AND COMBINATIONS-EXAMPLE
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  6. How many 3-digit even numbers can be formed from the digits 1, 2, 3, 4...

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  7. How many 3-digit even numbers can be formed from the digits 1, 2, 3, 4...

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  8. How many 3-digit numbers are there without repetition?

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  9. If 1/(6!)+1/(7!)=x/(8!), find x

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  10. Show that (2n)!/n!=[1.3.5……………….(2n-1)]2^n.

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  11. How many 4-digit numbers are there with no digit repeated?

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  16. If nC6=nC2, find ^nC2.

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  17. If 10Cr=^10C2 find the values of r.

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