The HCF and LCM of two numbers m and n are respectively 6 and 210. If m + n = 80, then 1/m + 1/n is equal to  Choose the correct option
A) 1 / 35 B) 3 / 35 C) 5 / 37 D) 4 / 63 E) none

Rationale: "answer we have , m x n = 6 x 210 = 1260 â ˆ ´ 1 / m + 1 / n = ( m + n ) / mn = 80 / 1260 = 4 / 63 correct option : d"
Answer: D