Adding and subtracting fractions

Advanced Math 4 · Unit 7 · fraction-add-sub · Teacher edition

fraction-add-sub

Name ______________________________Date ______________

1.
Compute $\dfrac{2}{3} + \dfrac{1}{4}$ .
Answer: ______________
2.
A ribbon is $4\dfrac{1}{4}$ m long. Maya cuts off $1\dfrac{5}{6}$ m for a bow. How much ribbon is left, in metres? Enter a fraction or mixed number.
Answer: ______________
3.
Priya paints $\dfrac{2}{5}$ of a fence on Saturday and $\dfrac{1}{4}$ of the same fence on Sunday. What fraction of the fence is painted after the two days?
1. (A)
  $\dfrac{3}{9}$
2. (B)
  $\dfrac{3}{20}$
3. (C)
  $\dfrac{13}{20}$
4. (D)
  $\dfrac{11}{20}$

Answer key — Adding and subtracting fractions

1.
11/12fraction-add-sub-01
$\frac{2}{3} + \frac{1}{4} = \frac{8}{12} + \frac{3}{12} = \mathbf{\frac{11}{12}}$ .
2.
29/12fraction-add-sub-02
$4\frac{1}{4} - 1\frac{5}{6} = 4\frac{3}{12} - 1\frac{10}{12} = 3\frac{15}{12} - 1\frac{10}{12} = 2\frac{5}{12}$ . Left: $\mathbf{\frac{29}{12}}$ m, that is $2\frac{5}{12}$ m. Check: $1\frac{10}{12} + 2\frac{5}{12} = 3\frac{15}{12} = 4\frac{3}{12}$ .
3.
(C)
$\dfrac{13}{20}$
fraction-add-sub-03
$\frac{2}{5} + \frac{1}{4} = \frac{8}{20} + \frac{5}{20} = \mathbf{\frac{13}{20}}$ . ( $\frac{3}{9}$ adds tops and bottoms — it is even less than $\frac{2}{5}$ alone; $\frac{3}{20}$ subtracts; $\frac{11}{20}$ renames $\frac{1}{4}$ as $\frac{3}{20}$ by mistake.)