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What is the smallest positive integer which is not a factor of the product \(264 \times 90 \times 1680\)?

  • A.12
  • B.13
  • C.14
  • D.15

Answer: B

The smallest positive integer that is not a factor is 13.

Factorise each number and combine:

\[ \begin{aligned} 264 &= 2^{3} \times 3 \times 11 \\ 90 &= 2 \times 3^{2} \times 5 \\ 1680 &= 2^{4} \times 3 \times 5 \times 7 \\ \text{product} &= 2^{8} \times 3^{4} \times 5^{2} \times 7 \times 11 \end{aligned} \]

Every integer from 1 to 12 is built from these primes within these powers, so all divide the product (12 = 22 × 3). 13 is a prime that does not occur, so it is not a factor. 14 = 2 × 7 and 15 = 3 × 5 are factors.

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