Question

The ratio between the HCF and LCM of 5, 15 and 20 is __________.

Answer 1

Prime factorisation of 5, 15 and 20 is

5 = 5
15 = 3 × 5
20 = 2 × 2 × 5

Thus, LCM of 5, 15 and 20 is 2 × 2 × 3 × 5 = 60
and HCF of 5, 15 and 20 is 5.

$$\begin{gathered} \mathrm{Therefore}, \\ \frac{\mathrm{HCF}}{\mathrm{LCM}}=\frac{5}{60}=\frac{1}{12} \end{gathered}$$

Hence, The ratio between the HCF and LCM of 5, 15 and 20 is 1 : 12.