Add & Subtract Within 1000 — Answer Key
Part A: Sort the Words
Sort each word or number into the correct category box.
1. Sort each problem by whether regrouping is NEEDED.
No regrouping
234+125200-100510+203 Needs regrouping
345+456432-219800-450 Regrouping is needed when a digit on top is smaller than the digit below it, or when a column adds to 10 or more. The problems 234+125, 200-100, and 510+203 do not need regrouping, while 345+456, 432-219, and 800-450 do need it.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. 234+125=359
4+5=9, 3+2=5, 2+1=3, so the sum is 359 with no regrouping.
2. 510+203=713
0+0=0 tens, 5+2=7 hundreds, 0+3=3 ones, so 510+203=713.
3. 600-400=200
6 hundreds minus 4 hundreds leaves 2 hundreds, which is 200.
4. 321+456=777
1+6=7, 2+5=7, 3+4=7, so the sum is 777.
5. 875-325=550
5-5=0, 7-2=5, 8-3=5, so 875-325=550.
Part C: True or False?
Read each statement. Circle True or False.
1. The problem 234+125 needs regrouping.
True False
4+5=9, 3+2=5, 2+1=3. No column reaches 10, so no regrouping is needed.
2. The problem 345+456 needs regrouping.
True False
5+6=11, which is more than 9, so you carry a 1 to the tens. Regrouping is needed.
3. The problem 432-219 needs borrowing.
True False
In the ones, 2 is smaller than 9, so you must borrow a ten to subtract.
4. Subtraction does not need regrouping when every top digit is bigger than the bottom digit.
True False
Borrowing is only needed when the top digit is smaller. If every top digit is bigger, you subtract column by column.