Ordering and Comparing Lengths
Order three objects by length and compare the lengths of two objects indirectly using a third object
What a learner can do afterwards
- Put three ribbons in order from shortest to longest
- Use a piece of string to compare the heights of two objects that cannot be placed side by side
- Explain that if A is longer than B and B is longer than C, then A is longer than C
1 · Read
You already know how to tell if one thing is longer than another. Now you will learn two new tricks: putting three things in order, and comparing two things that cannot sit side by side.
Mia has three pencils. She lines up the red pencil next to the blue pencil and sees the red one is shorter. Then she lines up the blue pencil next to the green pencil and sees the blue one is shorter too. So the order from shortest to longest is red, blue, green.
If one thing is longer than a second thing, and that second thing is longer than a third thing, then the first thing is longer than the third one too. You do not need to compare the first and the third directly.
To order things, compare them two at a time. And remember, if A is longer than B, and B is longer than C, then A is longer than C too.
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.
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.
Perimeter review
Perimeter is the walk around a shape. Add every side to find it. Squares have four equal sides.
Trace the edge with your finger. Add as you go. The total tells how much fence the shape needs.
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.
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2 · Watch
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Where it sits
Learn first
Where this leads
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.