Step-by-step Maths Level 3: Subtracting a 1-digit number with exchange

Method. Subtract the ones first. If the top digit is too small, exchange from the next column, then subtract.

1. Write the numbers in columns. Keep the ones under the ones and the tens under the tens.
   158 over 9
2. Exchange 1 ten for 10 ones. The ones on top (8) are fewer than the ones below (9), so we need more ones.
   5 tens become 4 tens, and the ones go from 8 to 18
3. Subtract the ones. 18 - 9 = 9.
   18 - 9 = 9
4. Subtract the tens. 4 - 0 = 4.
   4 - 0 = 4
5. Subtract the hundreds. 1 - 0 = 1.
   1 - 0 = 1
6. Write the answer. Read the columns from left to right.
   149

Check. Check: 149 + 9 = 158.

Watch out. Exchange a ten for ten ones when the ones on top are too small. Then take away.

Method. Subtract the ones first. If the top digit is too small, exchange from the next column, then subtract.

1. Write the numbers in columns. Keep the ones under the ones and the tens under the tens.
   987 over 9
2. Exchange 1 ten for 10 ones. The ones on top (7) are fewer than the ones below (9), so we need more ones.
   8 tens become 7 tens, and the ones go from 7 to 17
3. Subtract the ones. 17 - 9 = 8.
   17 - 9 = 8
4. Subtract the tens. 7 - 0 = 7.
   7 - 0 = 7
5. Subtract the hundreds. 9 - 0 = 9.
   9 - 0 = 9
6. Write the answer. Read the columns from left to right.
   978

Check. Check: 978 + 9 = 987.

Watch out. Exchange a ten for ten ones when the ones on top are too small. Then take away.

Method. Subtract the ones first. If the top digit is too small, exchange from the next column, then subtract.

1. Write the numbers in columns. Keep the ones under the ones and the tens under the tens.
   402 over 5
2. Exchange 1 hundred for 10 tens. There are no tens to take from, so we first change a hundred into tens.
   4 hundreds and 0 tens become 3 hundreds and 10 tens
3. Exchange 1 ten for 10 ones. The ones on top (2) are fewer than the ones below (5), so we need more ones.
   10 tens become 9 tens, and the ones go from 2 to 12
4. Subtract the ones. 12 - 5 = 7.
   12 - 5 = 7
5. Subtract the tens. 9 - 0 = 9.
   9 - 0 = 9
6. Subtract the hundreds. 3 - 0 = 3.
   3 - 0 = 3
7. Write the answer. Read the columns from left to right.
   397

Check. Check: 397 + 5 = 402.

Watch out. When a column is too small, exchange one from the column to its left. Ten ones make one ten, ten tens make one hundred.

Method. Subtract the ones first. If the top digit is too small, exchange from the next column, then subtract.

1. Write the numbers in columns. Keep the ones under the ones and the tens under the tens.
   916 over 9
2. Exchange 1 ten for 10 ones. The ones on top (6) are fewer than the ones below (9), so we need more ones.
   1 tens become 0 tens, and the ones go from 6 to 16
3. Subtract the ones. 16 - 9 = 7.
   16 - 9 = 7
4. Subtract the tens. 0 - 0 = 0.
   0 - 0 = 0
5. Subtract the hundreds. 9 - 0 = 9.
   9 - 0 = 9
6. Write the answer. Read the columns from left to right.
   907

Check. Check: 907 + 9 = 916.

Watch out. Exchange a ten for ten ones when the ones on top are too small. Then take away.

Method. Subtract the ones first. If the top digit is too small, exchange from the next column, then subtract.

1. Write the numbers in columns. Keep the ones under the ones and the tens under the tens.
   940 over 7
2. Exchange 1 ten for 10 ones. The ones on top (0) are fewer than the ones below (7), so we need more ones.
   4 tens become 3 tens, and the ones go from 0 to 10
3. Subtract the ones. 10 - 7 = 3.
   10 - 7 = 3
4. Subtract the tens. 3 - 0 = 3.
   3 - 0 = 3
5. Subtract the hundreds. 9 - 0 = 9.
   9 - 0 = 9
6. Write the answer. Read the columns from left to right.
   933

Check. Check: 933 + 7 = 940.

Watch out. Exchange a ten for ten ones when the ones on top are too small. Then take away.

Method. Subtract the ones first. If the top digit is too small, exchange from the next column, then subtract.

1. Write the numbers in columns. Keep the ones under the ones and the tens under the tens.
   847 over 9
2. Exchange 1 ten for 10 ones. The ones on top (7) are fewer than the ones below (9), so we need more ones.
   4 tens become 3 tens, and the ones go from 7 to 17
3. Subtract the ones. 17 - 9 = 8.
   17 - 9 = 8
4. Subtract the tens. 3 - 0 = 3.
   3 - 0 = 3
5. Subtract the hundreds. 8 - 0 = 8.
   8 - 0 = 8
6. Write the answer. Read the columns from left to right.
   838

Check. Check: 838 + 9 = 847.

Watch out. Exchange a ten for ten ones when the ones on top are too small. Then take away.

Method. Subtract the ones first. If the top digit is too small, exchange from the next column, then subtract.

1. Write the numbers in columns. Keep the ones under the ones and the tens under the tens.
   686 over 7
2. Exchange 1 ten for 10 ones. The ones on top (6) are fewer than the ones below (7), so we need more ones.
   8 tens become 7 tens, and the ones go from 6 to 16
3. Subtract the ones. 16 - 7 = 9.
   16 - 7 = 9
4. Subtract the tens. 7 - 0 = 7.
   7 - 0 = 7
5. Subtract the hundreds. 6 - 0 = 6.
   6 - 0 = 6
6. Write the answer. Read the columns from left to right.
   679

Check. Check: 679 + 7 = 686.

Watch out. Exchange a ten for ten ones when the ones on top are too small. Then take away.

Method. Subtract the ones first. If the top digit is too small, exchange from the next column, then subtract.

1. Write the numbers in columns. Keep the ones under the ones and the tens under the tens.
   383 over 9
2. Exchange 1 ten for 10 ones. The ones on top (3) are fewer than the ones below (9), so we need more ones.
   8 tens become 7 tens, and the ones go from 3 to 13
3. Subtract the ones. 13 - 9 = 4.
   13 - 9 = 4
4. Subtract the tens. 7 - 0 = 7.
   7 - 0 = 7
5. Subtract the hundreds. 3 - 0 = 3.
   3 - 0 = 3
6. Write the answer. Read the columns from left to right.
   374

Check. Check: 374 + 9 = 383.

Watch out. Exchange a ten for ten ones when the ones on top are too small. Then take away.

Method. Subtract the ones first. If the top digit is too small, exchange from the next column, then subtract.

1. Write the numbers in columns. Keep the ones under the ones and the tens under the tens.
   727 over 9
2. Exchange 1 ten for 10 ones. The ones on top (7) are fewer than the ones below (9), so we need more ones.
   2 tens become 1 tens, and the ones go from 7 to 17
3. Subtract the ones. 17 - 9 = 8.
   17 - 9 = 8
4. Subtract the tens. 1 - 0 = 1.
   1 - 0 = 1
5. Subtract the hundreds. 7 - 0 = 7.
   7 - 0 = 7
6. Write the answer. Read the columns from left to right.
   718

Check. Check: 718 + 9 = 727.

Watch out. Exchange a ten for ten ones when the ones on top are too small. Then take away.

Method. Subtract the ones first. If the top digit is too small, exchange from the next column, then subtract.

1. Write the numbers in columns. Keep the ones under the ones and the tens under the tens.
   748 over 9
2. Exchange 1 ten for 10 ones. The ones on top (8) are fewer than the ones below (9), so we need more ones.
   4 tens become 3 tens, and the ones go from 8 to 18
3. Subtract the ones. 18 - 9 = 9.
   18 - 9 = 9
4. Subtract the tens. 3 - 0 = 3.
   3 - 0 = 3
5. Subtract the hundreds. 7 - 0 = 7.
   7 - 0 = 7
6. Write the answer. Read the columns from left to right.
   739

Check. Check: 739 + 9 = 748.

Watch out. Exchange a ten for ten ones when the ones on top are too small. Then take away.

Method. Subtract the ones first. If the top digit is too small, exchange from the next column, then subtract.

1. Write the numbers in columns. Keep the ones under the ones and the tens under the tens.
   867 over 8
2. Exchange 1 ten for 10 ones. The ones on top (7) are fewer than the ones below (8), so we need more ones.
   6 tens become 5 tens, and the ones go from 7 to 17
3. Subtract the ones. 17 - 8 = 9.
   17 - 8 = 9
4. Subtract the tens. 5 - 0 = 5.
   5 - 0 = 5
5. Subtract the hundreds. 8 - 0 = 8.
   8 - 0 = 8
6. Write the answer. Read the columns from left to right.
   859

Check. Check: 859 + 8 = 867.

Watch out. Exchange a ten for ten ones when the ones on top are too small. Then take away.

Method. Subtract the ones first. If the top digit is too small, exchange from the next column, then subtract.

1. Write the numbers in columns. Keep the ones under the ones and the tens under the tens.
   601 over 4
2. Exchange 1 hundred for 10 tens. There are no tens to take from, so we first change a hundred into tens.
   6 hundreds and 0 tens become 5 hundreds and 10 tens
3. Exchange 1 ten for 10 ones. The ones on top (1) are fewer than the ones below (4), so we need more ones.
   10 tens become 9 tens, and the ones go from 1 to 11
4. Subtract the ones. 11 - 4 = 7.
   11 - 4 = 7
5. Subtract the tens. 9 - 0 = 9.
   9 - 0 = 9
6. Subtract the hundreds. 5 - 0 = 5.
   5 - 0 = 5
7. Write the answer. Read the columns from left to right.
   597

Check. Check: 597 + 4 = 601.

Watch out. When a column is too small, exchange one from the column to its left. Ten ones make one ten, ten tens make one hundred.

Method. Subtract the ones first. If the top digit is too small, exchange from the next column, then subtract.

1. Write the numbers in columns. Keep the ones under the ones and the tens under the tens.
   41 over 8
2. Exchange 1 ten for 10 ones. The ones on top (1) are fewer than the ones below (8), so we need more ones.
   4 tens become 3 tens, and the ones go from 1 to 11
3. Subtract the ones. 11 - 8 = 3.
   11 - 8 = 3
4. Subtract the tens. 3 - 0 = 3.
   3 - 0 = 3
5. Write the answer. Read the columns from left to right.
   33

Check. Check: 33 + 8 = 41.

Watch out. Exchange a ten for ten ones when the ones on top are too small. Then take away.

Method. Subtract the ones first. If the top digit is too small, exchange from the next column, then subtract.

1. Write the numbers in columns. Keep the ones under the ones and the tens under the tens.
   542 over 7
2. Exchange 1 ten for 10 ones. The ones on top (2) are fewer than the ones below (7), so we need more ones.
   4 tens become 3 tens, and the ones go from 2 to 12
3. Subtract the ones. 12 - 7 = 5.
   12 - 7 = 5
4. Subtract the tens. 3 - 0 = 3.
   3 - 0 = 3
5. Subtract the hundreds. 5 - 0 = 5.
   5 - 0 = 5
6. Write the answer. Read the columns from left to right.
   535

Check. Check: 535 + 7 = 542.

Watch out. Exchange a ten for ten ones when the ones on top are too small. Then take away.

Method. Subtract the ones first. If the top digit is too small, exchange from the next column, then subtract.

1. Write the numbers in columns. Keep the ones under the ones and the tens under the tens.
   573 over 8
2. Exchange 1 ten for 10 ones. The ones on top (3) are fewer than the ones below (8), so we need more ones.
   7 tens become 6 tens, and the ones go from 3 to 13
3. Subtract the ones. 13 - 8 = 5.
   13 - 8 = 5
4. Subtract the tens. 6 - 0 = 6.
   6 - 0 = 6
5. Subtract the hundreds. 5 - 0 = 5.
   5 - 0 = 5
6. Write the answer. Read the columns from left to right.
   565

Check. Check: 565 + 8 = 573.

Watch out. Exchange a ten for ten ones when the ones on top are too small. Then take away.

Method. Subtract the ones first. If the top digit is too small, exchange from the next column, then subtract.

1. Write the numbers in columns. Keep the ones under the ones and the tens under the tens.
   521 over 2
2. Exchange 1 ten for 10 ones. The ones on top (1) are fewer than the ones below (2), so we need more ones.
   2 tens become 1 tens, and the ones go from 1 to 11
3. Subtract the ones. 11 - 2 = 9.
   11 - 2 = 9
4. Subtract the tens. 1 - 0 = 1.
   1 - 0 = 1
5. Subtract the hundreds. 5 - 0 = 5.
   5 - 0 = 5
6. Write the answer. Read the columns from left to right.
   519

Check. Check: 519 + 2 = 521.

Watch out. Exchange a ten for ten ones when the ones on top are too small. Then take away.