90
Adding and subtracting fractions: problems
Textbook: Part 3, lesson 90, pp. 60–62
GoalWord problems on adding and subtracting fractions: writing and working out expressions.
New words
problem · masalaexpression · ifodaaltogether · jamileft over · qolgan
Explanation
In a fraction problem, first decide what to find: a total (add), what is left or a difference (subtract). Then write an expression and calculate by the rule. Write the answer with its unit. If the result is an improper fraction, it can also be written as a mixed number.
Worked examples
Two boards: 7/10 m and 5/10 m. Together 7/10 + 5/10 = 12/10 m = 1 2/10 m.
A jug had 11/5 l of milk and 4/5 l was drunk. What is left: 11/5 − 4/5 = 7/5 = 1 2/5 l.
Class activity
“Make up the problem”: children invent a real-life problem for the expression 7/9 + 4/9 and swap with a partner to solve.
Practice
1
A carpenter has two boards 7/10 m and 5/10 m long. Write the sum of their lengths.
12/10 = 1 2/10
2
A gift box needs 7/9 m of ribbon and a bunch of flowers needs 4/9 m. How many metres of ribbon in total?
11/9 = 1 2/9
3
A jug had 11/5 l of milk and 4/5 l was drunk. How much milk is left (l)?
7/5 = 1 2/5
4
From 30 kg of carrots 2/6 went into plov and 1/6 into salad. How many kilograms are left?
15
5
4/9 of the 72 pictures at an exhibition are about nature. How many pictures are about nature?
32