☰ Year plan · Mathematics

Term 2 review

Week 30 · Term 2 review · 3 lessons
1

Review: adding and subtracting fractions and mixed numbers

Discover Mathematics P5: Term 2, Units 7–12, Review
GoalReview adding and subtracting fractions and mixed numbers with unlike denominators.
New words
common denominator · a number that both denominators divide intomixed number · a whole number and a fraction together, like 2 1/4regroup · to borrow 1 whole and write it as a fraction, like 5 1/3 = 4 4/3
Explanation

To add or subtract fractions, first make the denominators the same. Then add or subtract the numerators and keep the denominator. Write the answer in simplest form. For mixed numbers, add or subtract the whole numbers and the fractions separately. If the fractions add to more than 1, change the extra into a whole number. If the first fraction is too small to subtract from, regroup: take 1 from the whole number and add it to the fraction. Example: 2/3 + 1/4 = 8/12 + 3/12 = 11/12. Example: 5 1/3 − 2 5/6 = 5 2/6 − 2 5/6 = 4 8/6 − 2 5/6 = 2 3/6 = 2 1/2.

StepDo this
1Make the denominators equal
2Add or subtract the numerators
3Regroup if needed
4Simplify the answer
Worked examples
3 1/2 + 2 3/4: whole numbers 3 + 2 = 5. Fractions 1/2 + 3/4 = 2/4 + 3/4 = 5/4 = 1 1/4. Total 5 + 1 1/4 = 6 1/4.
7/8 − 1/4 = 7/8 − 2/8 = 5/8.
A tank has 5 1/3 litres of water. Farida pours out 2 5/6 litres. 5 2/6 − 2 5/6 = 4 8/6 − 2 5/6 = 2 3/6 = 2 1/2 litres are left.
Class activity

Fraction duel. Each partner writes two mixed numbers on cards. Swap cards, add them and subtract them. Check each other's work by adding the difference back to the smaller number.

Practice
1
3/5 + 1/10 = ?
2
4 2/3 + 1 1/2 = ?
3
6 1/4 − 2 1/2 = ?
4
Rana buys 2 1/2 kg of tomatoes and 1 3/4 kg of cucumbers. How many kilograms does she buy altogether?
5
How much more are the tomatoes than the cucumbers?