Week 4 · Subtraction with regrouping and story problems · 3 lessons
3
Two-step stories with plus and minus
Discover Mathematics P4: Term 1, Unit 2, Lessons 5–7
GoalSolve stories that need two operations, plan the steps and check that the answer makes sense.
New words
two-step problem · a story that needs two calculations to find the answerestimate · a rounded answer used to check if the exact answer is reasonablereasonable · close to what we expected
Explanation
A two-step story has a hidden question. To solve it, ask three things. What do I know? What do I need to find first? What is the final question? Then do step 1, write its answer, and use it in step 2. The words give clues: left, fewer and spent mean subtract; altogether, more and joined mean add. Draw a bar model with three parts if it helps. At the end, estimate with rounded numbers to check. If the estimate is far from your answer, look for a mistake. Write the answer in a full sentence with the unit, such as LE or books.
Worked examples
A shop had 2,500 notebooks. It sold 840 in the morning and 765 in the afternoon. How many are left? Step 1: 840 + 765 = 1,605 sold. Step 2: 2,500 − 1,605 = 895 left. Estimate: 2,500 − 800 − 800 = 900, close to 895.
Step
Work
Result
1
1,250 − 175
1,075
2
1,075 + 240
1,315
A school has 1,250 pupils. In September 175 pupils moved to another school and 240 new pupils joined. How many pupils are there now? 1,250 − 175 = 1,075, then 1,075 + 240 = 1,315 pupils.
Farida had 5,000 LE. She paid 1,350 LE for a bicycle and 275 LE for a helmet. How much money is left? 1,350 + 275 = 1,625 LE spent. 5,000 − 1,625 = 3,375 LE left. Check: 3,375 + 1,625 = 5,000.
Class activity
Story workshop. Choose a topic from home, such as the grocery or the football club. Write a two-step story with a question at the end. Draw the bar model, solve it, and check by estimating. Let someone else solve your story and see if you agree.
Practice
1
Omar had 3,200 LE. He earned 1,450 LE and then spent 2,100 LE. How much does he have now?
3,200 + 1,450 = 4,650, then 4,650 − 2,100 = 2,550 LE.
2
A train had 1,840 passengers. At the first stop 560 got off, and at the second stop 395 got off. How many are still on the train?
