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If \ ^(15)C(3r)=\ \ ^(15)C(r+3)\ then\ r...

If `\ ^(15)C_(3r)=\ \ ^(15)C_(r+3)\ then\ r` is equal to a. 5 b. 4 c. 3 d. 2

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As
`\ ^(n)C_(x)= \ ^(n)C_(y)`
So,
`3r+r+3=15`
`4r+3=15`
`4r=12`
`r=3`
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