Idea 19of 23Builds onThe little 1 is a ten moved up
Unpack a ten to subtract
What do you do when a top digit is too small to subtract from?
Today you'll discover
- why you never flip the digits
- how to unpack a ten
- how to check by adding
Think first52 314 − 18 538, lined up by place
You need 4 ones − 8 ones. What do you do?
Decide first, then press Next. Watch the crossed-out digits.
52 314 above 18 538 in columns under the place names. In the ones column the 1 ten is crossed out to 0 and the 4 ones become 14, so 14 − 8 = 6. Every column then unpacks where it must, the answer reads 33 776, and the check reads 33 776 + 18 538 = 52 314. The last step asks for 63 205 − 27 461.
See the whole ideathe big idea and the key word, in one place
The big idea
When a top digit is too small, unpack 1 from the next place into ten.
Easy to get wrongNever flip a column to take the smaller digit from the larger. 4 − 8 is not 8 − 4.
Where it goes nextAdding checks subtracting: 33 776 + 18 538 = 52 314.
Key word
- unpack
- to trade 1 of a place for 10 of the place on its right, so there is enough to subtract
Ready to use it?
- Subtract five-digit numbers, unpacking where you need to.