Step-by-step Maths Level 4: Adding and subtracting in your head

Method. Change only the column that matches the number you add or take away.

1. Find the thousand digit in 5490. Only the thousand column changes, because 3000 is 3 thousands.
   5490 has 5 thousands
2. Take away 3 thousands. Change that digit only. The other digits stay the same.
   5 - 3 = 2
3. Write the answer. Check that the other digits are the same.
   2490

Check. Check: 2490 + 3000 = 5490.

Watch out. Adding or taking away a friendly number changes only one column, when no carry or exchange is needed.

Method. Change only the column that matches the number you add or take away.

1. Find the thousand digit in 6811. Only the thousand column changes, because 2000 is 2 thousands.
   6811 has 6 thousands
2. Add 2 thousands. Change that digit only. The other digits stay the same.
   6 + 2 = 8
3. Write the answer. Check that the other digits are the same.
   8811

Check. Check: 8811 - 2000 = 6811.

Watch out. Adding or taking away a friendly number changes only one column, when no carry or exchange is needed.

Method. Change only the column that matches the number you add or take away.

1. Find the thousand digit in 8853. Only the thousand column changes, because 3000 is 3 thousands.
   8853 has 8 thousands
2. Take away 3 thousands. Change that digit only. The other digits stay the same.
   8 - 3 = 5
3. Write the answer. Check that the other digits are the same.
   5853

Check. Check: 5853 + 3000 = 8853.

Watch out. Adding or taking away a friendly number changes only one column, when no carry or exchange is needed.

Method. Change only the column that matches the number you add or take away.

1. Find the thousand digit in 2338. Only the thousand column changes, because 2000 is 2 thousands.
   2338 has 2 thousands
2. Add 2 thousands. Change that digit only. The other digits stay the same.
   2 + 2 = 4
3. Write the answer. Check that the other digits are the same.
   4338

Check. Check: 4338 - 2000 = 2338.

Watch out. Adding or taking away a friendly number changes only one column, when no carry or exchange is needed.

Method. Change only the column that matches the number you add or take away.

1. Find the hundred digit in 5704. Only the hundred column changes, because 100 is 1 hundreds.
   5704 has 7 hundreds
2. Add 1 hundreds. Change that digit only. The other digits stay the same.
   7 + 1 = 8
3. Write the answer. Check that the other digits are the same.
   5804

Check. Check: 5804 - 100 = 5704.

Watch out. Adding or taking away a friendly number changes only one column, when no carry or exchange is needed.

Method. Change only the column that matches the number you add or take away.

1. Find the ten digit in 2861. Only the ten column changes, because 20 is 2 tens.
   2861 has 6 tens
2. Add 2 tens. Change that digit only. The other digits stay the same.
   6 + 2 = 8
3. Write the answer. Check that the other digits are the same.
   2881

Check. Check: 2881 - 20 = 2861.

Watch out. Adding or taking away a friendly number changes only one column, when no carry or exchange is needed.

Method. Change only the column that matches the number you add or take away.

1. Find the ten digit in 7591. Only the ten column changes, because 30 is 3 tens.
   7591 has 9 tens
2. Take away 3 tens. Change that digit only. The other digits stay the same.
   9 - 3 = 6
3. Write the answer. Check that the other digits are the same.
   7561

Check. Check: 7561 + 30 = 7591.

Watch out. Adding or taking away a friendly number changes only one column, when no carry or exchange is needed.

Method. Change only the column that matches the number you add or take away.

1. Find the ten digit in 7918. Only the ten column changes, because 50 is 5 tens.
   7918 has 1 tens
2. Add 5 tens. Change that digit only. The other digits stay the same.
   1 + 5 = 6
3. Write the answer. Check that the other digits are the same.
   7968

Check. Check: 7968 - 50 = 7918.

Watch out. Adding or taking away a friendly number changes only one column, when no carry or exchange is needed.

Method. Change only the column that matches the number you add or take away.

1. Find the hundred digit in 7469. Only the hundred column changes, because 100 is 1 hundreds.
   7469 has 4 hundreds
2. Add 1 hundreds. Change that digit only. The other digits stay the same.
   4 + 1 = 5
3. Write the answer. Check that the other digits are the same.
   7569

Check. Check: 7569 - 100 = 7469.

Watch out. Adding or taking away a friendly number changes only one column, when no carry or exchange is needed.

Method. Change only the column that matches the number you add or take away.

1. Find the hundred digit in 6650. Only the hundred column changes, because 400 is 4 hundreds.
   6650 has 6 hundreds
2. Take away 4 hundreds. Change that digit only. The other digits stay the same.
   6 - 4 = 2
3. Write the answer. Check that the other digits are the same.
   6250

Check. Check: 6250 + 400 = 6650.

Watch out. Adding or taking away a friendly number changes only one column, when no carry or exchange is needed.

Method. Change only the column that matches the number you add or take away.

1. Find the ten digit in 9091. Only the ten column changes, because 30 is 3 tens.
   9091 has 9 tens
2. Take away 3 tens. Change that digit only. The other digits stay the same.
   9 - 3 = 6
3. Write the answer. Check that the other digits are the same.
   9061

Check. Check: 9061 + 30 = 9091.

Watch out. Adding or taking away a friendly number changes only one column, when no carry or exchange is needed.

Method. Split one number, then add the parts in stages.

1. Split the second number. Think of the hundreds part and the rest.
   765 = 700 + 65
2. Add the hundreds first. Add the thousands and hundreds together.
   6856 + 700 = 7556
3. Add the rest. Then add the last part.
   7556 + 65 = 7621
4. Write the answer. This is the total.
   7621

Check. Check: 7621 - 765 = 6856.

Watch out. Adding in stages is quicker than writing the sum in columns, when the numbers are friendly.

Method. Change only the column that matches the number you add or take away.

1. Find the thousand digit in 9890. Only the thousand column changes, because 3000 is 3 thousands.
   9890 has 9 thousands
2. Take away 3 thousands. Change that digit only. The other digits stay the same.
   9 - 3 = 6
3. Write the answer. Check that the other digits are the same.
   6890

Check. Check: 6890 + 3000 = 9890.

Watch out. Adding or taking away a friendly number changes only one column, when no carry or exchange is needed.

Method. Change only the column that matches the number you add or take away.

1. Find the thousand digit in 8517. Only the thousand column changes, because 2000 is 2 thousands.
   8517 has 8 thousands
2. Take away 2 thousands. Change that digit only. The other digits stay the same.
   8 - 2 = 6
3. Write the answer. Check that the other digits are the same.
   6517

Check. Check: 6517 + 2000 = 8517.

Watch out. Adding or taking away a friendly number changes only one column, when no carry or exchange is needed.

Method. Change only the column that matches the number you add or take away.

1. Find the thousand digit in 8619. Only the thousand column changes, because 3000 is 3 thousands.
   8619 has 8 thousands
2. Take away 3 thousands. Change that digit only. The other digits stay the same.
   8 - 3 = 5
3. Write the answer. Check that the other digits are the same.
   5619

Check. Check: 5619 + 3000 = 8619.

Watch out. Adding or taking away a friendly number changes only one column, when no carry or exchange is needed.

Method. Split one number, then add the parts in stages.

1. Split the second number. Think of the hundreds part and the rest.
   732 = 700 + 32
2. Add the hundreds first. Add the thousands and hundreds together.
   2627 + 700 = 3327
3. Add the rest. Then add the last part.
   3327 + 32 = 3359
4. Write the answer. This is the total.
   3359

Check. Check: 3359 - 732 = 2627.

Watch out. Adding in stages is quicker than writing the sum in columns, when the numbers are friendly.