Idea 19of 22Builds onDecimals in measurements
Move the digits to change the unit
Is there a quick way to see 28.5 km in metres?
Today you'll discover
- how many steps apart two units are
- which way the digits move
- where the zeros come from
Think first28.5 km in a place-value chart
28.5 km is how many metres?
Decide first, then press Next. Watch the digits, not the point.
The length units in a row, km to mm, with × 10 arrows. Under them, a place-value chart from ten thousands to hundredths with 28.5 in it: 2 in the tens, 8 in the ones, 5 in the tenths, and km highlighted. Then the three arrows from km to m light up and each digit slides 3 places left, with zeros filling the tens and ones: 28 500 m. The last step shows 2.4 kg.
See the whole ideathe big idea and the key word, in one place
The big idea
Multiplying by 1000 moves every digit 3 places left: 28.5 km = 28 500 m.
One place for each step
Each step of × 10 moves the digits one place left.
- km28.5
- × 10285
- × 1002850
- × 1000: m28 500
Easy to get wrongAdding zeros after the point changes nothing: 28.5000 is still 28.5. Move the digits instead.
Key word
- digit shift
- moving every digit the same number of places, to multiply or divide by 10, 100 or 1000
Ready to use it?
- Convert with a place-value chart.
- Say how many places the digits move.