Discussion
The LCM of 21, 36, and 66 is not a multiple of :
Answer: C
The LCM is not a multiple of 72.
Factorise each number and take the highest power of every prime:
\[ \begin{aligned} 21 &= 3 \times 7 \\ 36 &= 2^{2} \times 3^{2} \\ 66 &= 2 \times 3 \times 11 \\ \text{LCM} &= 2^{2} \times 3^{2} \times 7 \times 11 = 2772 \end{aligned} \]
72 is \(2^{3} \times 3^{2}\), but the LCM has only \(2^{2}\), so 2772 is not a multiple of 72 (\(2772 \div 72 = 38.5\)).
The others divide it exactly: \(2772 \div 42 = 66\), \(2772 \div 28 = 99\) and \(2772 \div 44 = 63\).
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