Choosing a tool or representation
Select and use appropriate tools and representations (number lines, hundred squares, rulers, part-whole models) to support problem-solving
What a learner can do afterwards
- Choose a number line or hundred square to support adding or subtracting two-digit numbers
- Select a ruler when a problem requires measuring length
- Explain why one representation (e.g. a number line vs cubes) is more helpful for a particular problem
1 · Read
Not every problem is best solved in your head. A number line, a hundred square, or a ruler can help you see the answer instead of guessing.
A number line lets you hop from one number to another, so it fits adding and subtracting. A hundred square lays every number out in rows of ten, so adding ten means dropping one row straight down. Both tools show each step, so you do not lose track while you count.
Mia needs to measure her book, so she picks up a ruler, not a number line, because a ruler is made for measuring length. Then Mia needs to add 36 and 20, so she picks a hundred square and counts on two rows.
Ask yourself: am I measuring something, or am I adding and subtracting numbers? That tells you which tool to reach for.
Pick the tool that matches the problem: a ruler for length, a number line or hundred square for adding and subtracting.
More to read
Measuring lengths with different units
Different units fit different things. Small lengths use centimetres. Longer walks use metres. Tiny spoons use millilitres.
Try measuring your desk. Line up the ruler at zero and read the number at the end. Write the unit too, like 30 cm.
11.1: Introducing Double Number Line Diagrams
A number line shows order. Numbers grow to the right. Jumps show adding or taking away.
Use it for sums within 100. Start at the first number, jump forward to add. Land on the answer and check with blocks.
Intro to place value: FAQ
Place value tells what each digit is worth. In 47, the 4 means 40 and the 7 means 7. Tens are bigger than ones.
Use blocks to see it. Four ten sticks and seven single cubes make 47. Add ten and only the tens digit grows.
1.7: Measuring Mass, Length, and Volume
We measure to know how much. Length uses rulers and centimetres. Mass uses scales and grams. Capacity uses jugs and millilitres.
Pick the right tool for the job. Long tables need rulers. Heavy bags need scales. Juice needs a measuring jug.
Explore more
2 · Watch
به انگلیسیTake it off screen
Where it sits
Learn first
Optional connections
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.