adding fractions with different denominators

Question

How do I add fractions with different denominators. I know I have to find the least common denominator but can someone explain how to do that? Here is a problem:

1/3 + 2/5 + 5/7

Answer 1

Given 1/3 + 2/5 + 5/7

Least common denominator to 3,5,7 is =3*5*7

= 105

1/3+2/5+5/7 = 1*35+2*21+5*15/105

= 35+42+75/105

= 152/105