Add and subtract fractions that have different denominators

The least common denominator (LCD) for a set of fractions is the smallest number each denominator will divide exactly (divide with no remainder)

$\frac35 + \frac13$

$\frac17 + \frac23$

$\frac52 - \frac73$

$\frac25 - \frac{11}{15}$

If the smaller denominator is a factor of the larger denominator

$-5 + \frac34$