# Find the LCD to add and subtract fractions

When we add or subtract fractions that have different denominators, the least common denominator is not always obvious
QUESTION OF
calculate
Questions #: 4
Time: 5 minutes
Pass Score: 80.0%
Style
Mode

#### The Least Common Multiple (LCM)

The least common multiple (LCM) of two whole numbers is the smallest whole number that is divisible by both of those numbers

POINTS (1)

#### Finding the least common denominator

Choose the right way to find the LCM of the denominators

Write the multiples of the largest denominator in increasing order, until one is found that is divisible by the other denominators.
Prime factor each denominator. The LCM is a product of prime factors, where each factor is used the greatest number of times it appears in any one factorization.
POINTS (1)

#### Add the following fractions and simplify if possible

$\frac{7}{15} + \frac{3}{10}$

POINTS (1)

#### Subtract and simplify the following two fractions

$\frac{13}{28} - \frac{1}{21}$

POINTS (1)