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Mathematics: relationships for creating · Lesson 02 / 08

An estimate raises a flag

Four paper strips are 19 cm long each. Someone calculated a total of 760 cm. Before repeating the calculation, an estimate can reveal a mismatch.

Learning paths8 min

Let's discover together

  1. 1

    19 cm is close to 20 cm. Four groups of about 20 cm make about 80 cm. Here we rounded each strip upward.

  2. 2

    The exact calculation is 4 × 19 = 76 cm. Another way: 4 × 20 − 4 × 1 = 80 − 4 = 76. The estimate 80 was 4 cm too high.

  3. 3

    One metre has 100 centimetres. So 76 cm is less than 1 m. Do not add 76 cm and 1 m as though they were 77 of the same unit: convert first.

  4. 4

    Estimates help detect large errors; they do not prove the exact result. When a measurement decides whether something fits, check the precision needed.

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YOUR MISSION

Estimate a quantity, calculate the exact value and check units.

Now it's your turn

Discovery workshop

The paper-strip workshop

4 strips of 19 cm. To estimate, use 20 cm per strip.
Build your answers and check when you are ready.
A moment to understand

The estimate is close to the calculation. What can we conclude?

I need a hint

Approximating helps you check; it does not make an estimate exact.

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Take it with you

Estimate 6 × 28 before calculating. Record your approximation, exact result and why they differ. Use only invented measurements.

At your own pace

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