Let HCF = N
According to the question, LCM = 20N
Given that, HCF + LCM = 2520
⇒ N + 20N = 2520
⇒ N = 2520 / 21 = 120
Now, LCM = 20N = 20 x 120 = 2400
We know that,
1st number x 2nd number = HCF x LCM
⇒ 2nd number = (LCM x HCF) / (1st number)
= (120 x 2400) / 480 = 600
∴ Required answer = 600 x 3 = 1800