There has to be a common denominator in order to add fraction.
1 / a + b and 5 / 2 ( a + b)
the common denominator would be 2(a+b) therefore multiple thé first fraction by 2, and the second by 1.
2 / 2(a + b) + 5 / 2(a + b)
2 + 5 = 7
the denominator stays the same
so 7 / 2(a + b)
