Idea 20of 23Builds onUnpack a ten to subtract
Subtract across zeros
How do you unpack when the next places are all zeros?
Today you'll discover
- where the unpacking starts
- why the zeros turn into 9s
- how to check the answer
Think first40 006 − 2 358
You need more ones, but the tens, hundreds and thousands are 0. Where does the unpacking start?
Decide first, then press Next. Find the first digit that is not 0.
40 006 above 2 358 in columns. The ones column is outlined; the 4 is crossed out to 3, each 0 crossed out to 9, and the 6 ones become 16. Then every column is subtracted: 37 648, with the check 37 648 + 2 358 = 40 006. The last step asks for 30 000 − 12 745.
See the whole ideathe big idea and the key word, in one place
The big idea
Across zeros, unpack from the first digit that is not 0; each zero becomes 9.
40 006, unpacked
The same number, built so every column can subtract.
- ten thousands3
- thousands9
- hundreds9
- tens9
- ones16
Key word
- subtract across zeros
- to unpack from the first digit that is not 0, turning each 0 in between into 9
Ready to use it?
- Subtract from a number with zeros in it.