Transcript How to Subtract two-digit numbers with regrouping

How to Subtract two-digit
numbers with regrouping
By: Melissa Collins
How do you know when to
subtract?
In order to subtract, you need to decide if you need
to regroup. To decide if you need to regroup
follow these 8 steps.
Step 1
• You look at the problem and look to see if it is a
subtraction problem. If it is, move to step 2.
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-13
Step 2
• If it is a subtraction problem you always start in
the ones column. If the bottom number is bigger
then you must regroup.
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-17
Step 3
• If the bottom number isn’t bigger then you just
subtract the ones.
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- 14
Step 4
• If the bottom number is bigger then you need to
knock on Mr. Ten’s door. Ask Mr. Ten if you can
borrow one ten.
Step 5
• When you borrow one ten from Mr. Ten you cross
out the number in the tens and subtract 1 away
from that number. Now, write the new number
above the number that you crossed out.
2
34
-17
Step 6
• Since you borrowed a ten, you now add 10 to the
top number in the ones column. So, instead of 4
ones you now have 14 ones. Next, cross out the 4
and write 14 above it. You can also simply just
write a 1 in front of the 4 to make it 14.
2 14
3 4
-1 7
Step 7
• Now you can subtract the ones. If you have 14,
and you give me 7, how many will you have left?
2 14
3 4
-1 7
7
Step 8
• After you subtract the ones, look at the bottom
number in the tens column. If that number is
smaller than the top number, then subtract the
tens.
2
3
-1
1
14
4
7
7
It’s your turn to
practice!
Remember you always start in the ones. You look
at the bottom number, if the bottom number is
bigger than you must regroup.
Question 1
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-29
A. 22
B. 28
C. 18
Question 2
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-21
A. 22
B. 23
C. 32
Question 3
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-15
A. 18
B. 22
C. 48
Are you a Star
Mathematician?
•
You’re a Star Mathematician if all your answers are correct.
•
If 2 out of 3 problems are correct, then, your on your way to being
a Star Mathematician. In order to be a Star Mathematician you
need to practice 2 subtraction problems daily.
•
If 1 or none are correct out of 3, you need to practice, practice,
and practice to be a Star Mathematician. You need to do 4
subtraction problems daily.
Nice Try
• Sorry but you missed that one.
• Go back and take another look.
• Question 1
• Question 2
• Question 3
Congratulations
• Great job! Keep up the good work!
• Question 2
• Question 3
• I answered all 3 questions.