If LCM(a, b) = 21

We know that, LCM(a, b) × HCF(a, b) = a × b

⇒ 210 × 6 = ab

⇒ ab = 1260

OR

We know that, for a rational number to have a terminating decimal expansion, q should be of the form = 2^a × 5^b

Therefore, in a given number , denominator 2500 can be factorised as,

2500 = 2 × 2 × 5 × 5 × 5 × 5

2500 = 2² × 5⁴

As 2500 can be expressed as 2² × 5⁴, it will have a terminating decimal expansion.