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If $6=2\times 3$ and $20=2^2\times 5$, then their HCF and LCM respectively are
A$2$ and $30$
B$2$ and $60$
C$6$ and $20$
D$1$ and $120$
Answer & Solution
Correct answer: B. $2$ and $60$
The common prime factor is only $2$, and the smallest power common to both numbers is $2^1$, so $\operatorname{HCF}=2$. For the LCM, take the greatest powers of all primes involved: $2^2\times 3\times 5=60$.
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