### Home > MC1 > Chapter 7 > Lesson 7.2.4 > Problem7-82

7-82.

Find common denominators and calculate each of the following sums.

1.  $\frac { 3 } { 8 } + \frac { 1 } { 4 }$

Remember, the denominator is the bottom number of a fraction. Here the denominators are $8$ and $4$. Can you change the fractions so that both denominators are $8$?

$\frac{5}{8}$

2.  $\frac { 2 } { 5 } + \frac { 1 } { 3 }$

Here, you might like to find the least common multiple of $5$ and $3$. This number should eventually be your common denominator.

$3$ and $5$ have a least common multiple of $15$.
Use multiplication to convert $\frac{2}{5}$ and $\frac{1}{3}$ to fractions with a denominator of $15$.
If $\frac{2}{5}+\frac{1}{3}=\frac{6}{15}+\frac{5}{15}$ , can you find the final sum?
3. What is the least common multiple of $8$ and $4$? Of $5$ and $3$?
Notice that $8$ is a multiple of $4$. Refer to part (b) for the least common multiple of $3$ and $5$.