Which of the following rational numbers have a terminating decimal expansion?

A number of the form $\frac{p}{q}$ has a terminating decimal expansion if the denominator (q) can be expressed as 2ⁿ5^m, where m and n are non-negative integers. 

The rational number  $\frac{420}{240}$ can be written as 

$\frac{420}{240}=\frac{2\times 2\times 3\times 5\times 7}{2\times 2\times 2\times 2\times 3\times 5}=\frac{7}{2^2\times 5^0}$ 

Here, the denominator is of the form 2ⁿ5^m, where n = 2 and m = 0. 

Thus, $\frac{420}{240}$ has a terminating decimal expansion.