20 − 5
Common Core 2.NBT.B.5
Subtraction across a zero
A zero in the ones place means there are no ones to take. Break one ten into ten ones first. The tens digit goes down by one, and the ones become 10. Then subtract.
One worked example
50 − 26
- The ones digit is 0, so trade a ten.
- 5 tens become 4 tens, and the ones become 10.
- 10 − 6 = 4 and 4 − 2 = 2. The difference is 24.
Answer: 24
Subtract within 100, including from a multiple of ten.
Easy
Subtract. Break a ten when the ones digit is 0.
50 − 29
60 − 54
80 − 11
50 − 18
60 − 47
Answer key
- 15
- 21
- 6
- 69
- 32
- 13
Medium
Subtract. Break a ten when the ones digit is 0.
50 − 16
80 − 26
50 − 37
60 − 46
60 − 18
80 − 2
40 − 21
50 − 22
30 − 19
Answer key
- 34
- 54
- 13
- 14
- 42
- 78
- 19
- 28
- 11
Hard
Subtract. Break a ten when the ones digit is 0.
40 − 39
90 − 55
30 − 29
60 − 12
70 − 69
70 − 14
30 − 24
40 − 16
80 − 49
30 − 5
50 − 19
30 − 21
Answer key
- 1
- 35
- 1
- 48
- 1
- 56
- 6
- 24
- 31
- 25
- 31
- 9
Related skills
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