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\(2 + {}^{15}C_{1} + {}^{15}C_{2} + \ldots {}^{15}C_{14} =\)

  • A.\(2^{14}\)
  • B.\(2^{15}\)
  • C.\(2^{16}\)
  • D.\(2^{10}\)
  • E.\(2^{18}\)

Answer: B

The sum is \(2^{15}\).

The sum of all binomial coefficients of order 15 is \(2^{15}\):

\[ \begin{aligned} &{}^{15}C_{0} + {}^{15}C_{1} + \cdots + {}^{15}C_{15} \\ &= 2^{15} \end{aligned} \]

The given expression is missing only \({}^{15}C_{0}\) and \({}^{15}C_{15}\), each equal to 1, and the leading 2 supplies exactly these. So it equals the full sum, \(2^{15}\). \(2^{14}\) would be the sum of the even-index (or odd-index) coefficients alone, and \(2^{16}\) belongs to order 16.

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