1
Kilogram story problems
Discover Mathematics P2: Term 1, Lessons 51–60
GoalSolve add and take-away story problems about mass and write the unit in the answer.
New words
in all · all the parts put togetherleft · what remains after taking awaynumber sentence · a short math sentence with numbers and a signunit · the word after a number, like g or kg
Explanation
Mass problems are solved like other story problems. Read the story. Decide if you are putting parts together (add) or taking a part away (subtract). Write a number sentence and solve it. Then write the unit in your answer. A bag of onions weighs 14 kg and a bag of potatoes weighs 8 kg. How much do they weigh together? Add: 14 + 8 = 22. The answer is 22 kg. Never forget kg or g after the number.
| Step | What to do |
|---|---|
| 1. Read | Find the numbers and the question |
| 2. Decide | Add (+) or take away (−)? |
| 3. Solve | Write the number sentence |
| 4. Unit | Write g or kg in the answer |
Worked examples
A bag of onions is 14 kg and a bag of potatoes is 8 kg. 14 + 8 = 22 kg together.
A box holds 60 g of dates. Malak eats 25 g. 60 − 25 = 35 g are left.
Dina buys 7 kg of tomatoes, 6 kg of cucumbers and 5 kg of onions. 7 + 6 = 13, then 13 + 5 = 18 kg in all.
Class activity
Market play. Use paper price tags: tomatoes 4 kg, onions 6 kg, potatoes 9 kg, lemons 3 kg. The grown-up plays the shopper and says things like ‘I want the tomatoes and the potatoes’. The child is the seller and says how many kg that is in all, then how many kg more potatoes than lemons.
Practice
1
A sack of rice is 25 kg and a sack of beans is 18 kg. How much do they weigh together?
25 + 18 = 43 kg.
2
Seif has 90 g of sugar. He uses 40 g. How much sugar is left?
90 − 40 = 50 g.
3
Ahmed weighs 31 kg and his sister weighs 27 kg. How much heavier is Ahmed?
31 − 27 = 4 kg.
4
One box has 38 g of raisins and another has 45 g. How many grams in all?
38 + 45 = 83 g.
5
Write the number sentence with its unit: 52 kg take away 17 kg.
52 − 17 = 35 kg.