SEARCH HOME
 Math Central Quandaries & Queries
 Question from Kathy, a parent: 1 3/4 + 1 2/3= ? 5 1/2 - 2 5/6= ?

Hi Kathy,

I'm going to illustrate the procedure by doing a similar question

$3 \frac25 + 2 \frac38.$

First of all $3 = \large \frac{3 \times 5}{5} = \frac{15}{5}.$ Similarly $2 = \large \frac{16}{8}$ and hence

$3 \frac25 + 2 \frac38\ = \frac{15}{5} + \frac25 + \frac{16}{8} + \frac38\ = \frac{17}{5} + \frac{19}{8}.$

To add $\large \frac{17}{5}$ and $\large \frac{19}{8}$ I ned the two fractions to have a common denominator. I can find a common denominator by multiplying the two denominators and hence $5 \times 8 = 40$ is a common denominator. Thus

$\frac{17}{5} + \frac{19}{8} = \frac{17 \times 8}{5 \times 8} + \frac{19 \times 5}{8 \times 5} = \frac{136}{40} + \frac{95}{40} = \frac{231}{40}.$