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A question paper consists of five problems, each problem having three internal choices. In how many ways can a candidate attempt one or more problems?

  • A.63
  • B.511
  • C.1023
  • D.15

Answer: C

For each problem the candidate has four options: attempt one of the three internal choices, or leave the problem alone.

\[ 4^{5} = 1024 \]

One of those is attempting nothing at all, which the question excludes:

\[ 1024 - 1 = 1023 \]

The 511 on offer comes from \( 2^{9} - 1 \) and ignores the internal choices.

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