Hong Kong
Stage 2

# Adding and Subtracting fractions (easily related denominators)

Lesson

Adding fractions with easily related denominators requires us to know the equivalent fractions for our benchmarks.

In this applet, the red and blue fractions are related.   It will allow you to see visually the size of the fractions and what the common denominator is.

You should be able to easily recognise some equivalent fractions and then calculate the addition or subtraction necessary.

#### Example

##### Question 1

Question: Add $3$3 tenths and $1$1 fifth.

Think: From my fraction calculator I know that $1$1 fifth is the same as $2$2 tenths.

Do: So this question is really asking me to add $3$3 tenths and $2$2 tenths which is $5$5 tenths.

I could leave this fraction as $5$5 tenths, however I also know that $5$5 tenths is the same as $1$1 half.

##### Question 2

Question: Evaluate $\frac{7}{3}-\frac{7}{6}$7376

Think: I know that $\frac{1}{3}$13 is the same as $\frac{2}{6}$26.

Do: So this question is really asking me to do $\frac{14}{6}-\frac{7}{6}$14676 which is $\frac{7}{6}$76.

I could leave this fraction as $\frac{7}{6}$76 or change to $1\frac{1}{6}$116.

##### QUESTION 3

Evaluate $\frac{1}{3}+\frac{1}{6}$13+16.

##### QUESTION 4

Evaluate $\frac{3}{8}-\frac{1}{4}$3814.

##### QUESTION 5

Using fractions, evaluate "two sevenths plus five sevenths".