Adding and subtracting (age 10+)
Solve addition and subtraction multi-step problems in contexts, deciding which operations and methods to use and why, with numbers up to 10,000,000 and decimals
What a learner can do afterwards
- Solve a two-step word problem involving addition and subtraction of numbers beyond 1,000,000
- Choose between mental, written, and calculator methods for a multi-step problem and justify the choice
- Interpret a real-life context to identify which addition/subtraction operations are needed across multiple steps
1 · Read
You can already read big numbers like 4,302,561, and many real problems ask you to do more than one step with numbers that big. You might add then subtract, subtract twice, or add twice then subtract. Read the problem slowly and work out what happens, in order, before you start calculating. For huge or tangled numbers use a written method. For small simple numbers use mental math. Round first to estimate and check.
A charity raised $3,450,750 in the spring and $2,180,600 in the autumn. Later, they spent $1,975,300 on new equipment. First add the two amounts they raised: $3,450,750 + $2,180,600 = $5,631,350. Then subtract what they spent: $5,631,350 - $1,975,300 = $3,656,050 left.
For huge numbers or tricky decimals, a written method or calculator is safer than doing it in your head. Whichever method you pick, round the numbers first to estimate the answer, so you can check your real answer makes sense.
Break a multi-step problem into its steps, pick the best method for the numbers involved, and check your answer against an estimate.
The rewritten reading was written for this dataset.
2 · Watch
Take it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
17 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.