LCM of a fraction means
(LCM of numerator/HCF of denominatior).
here,
$$25=5^2,15=5×3,20=5×2^2$$
and $$21=3×7,28=7×2^2$$
So,LCM(25,15,20)=$$5×3×2^2=300$$
and
HCF(7,21,28)=7.
So, required LCM=(300/7).
A is correct choice.
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