Two-step addition and subtraction problems
Solve addition and subtraction two-step problems in contexts, deciding which operations and methods to use and why
What a learner can do afterwards
- Identify the two steps needed to solve a contextual problem
- Choose between mental and written methods for each step based on the numbers
- Explain why the chosen operations and methods are appropriate
1 · Read
Some problems need more than one calculation. You work out the first part, then use that answer to work out the second part. That's a two-step problem.
Zara has $10. She buys a pencil for $3 and an eraser for $2. Step 1: add the prices, 3 + 2 = 5. That's what she spent. Step 2: subtract that from her $10, 10 - 5 = 5. Zara gets $5 change.
Look at the numbers before you pick a method. Small, round numbers are quick to add in your head. Bigger or trickier numbers are safer to write down step by step.
Before you calculate, plan both steps and think about why each one makes sense. That way your answer fits the problem.
Break the problem into two steps, solve the first, then use that answer for the second.
More to read
1.2 Add Whole Numbers
Word problems hide two jobs in one story. A shop sells some apples, then new apples arrive. That is a take away followed by an add.
Spot each job before touching numbers. The apple story needs 250 - 120 first, then the answer plus 80.
1.3 Subtract Whole Numbers
Order matters in two step stories. On a bus, 25 people get off first, then 38 get on. Work left to right through the story.
Ben and his stickers follow the same shape: 95 - 30 = 65, then 65 + 45 = 110. Each answer feeds the next step.
Add and subtract within 20: FAQ
Pick an easy method for each step. Small friendly numbers like 130 + 80 suit quick mental maths. Tricky numbers like 4867 - 2999 deserve a written column.
Matching the method to the numbers saves time and slips.
Addition, subtraction, and estimation: FAQ
Check that each operation fits its story line. New arrivals mean add, because the total grows. People leaving mean subtract.
Ask why at every step. If the reason is sound, the operation is sound.
Explore more
2 · Watch
به انگلیسیTake it off screen
Where it sits
This opens up
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
18 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.