For what value of \(n\) is \(^{n+1}C_{3} = 4 \cdot ^{n}C_{3}\)?

  • A 6
  • B 5
  • C 4
  • D 3

The correct answer is D. 3

Given that \(^{n+1}C_{3} = 4 \cdot ^{n}C_{3}\), we can write this as:

\(\frac{(n+1)!}{3!(n+1-3)!} = 4 \cdot \frac{n!}{3!(n-3)!}\)

Simplifying both sides of the equation:

\(\frac{(n+1)(n)(n-1)(n-2)}{6} = 4 \cdot \frac{n(n-1)(n-2)}{6}\)

Now, we can cancel out the common factors:

\((n+1) = 4\)

So, \(n = 3\).

Therefore, the answer is 3

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