Adding and Subtracting Decimals

Adding decimals is easy when you keep your work neat

To add decimals, follow these steps:

Example: Add 1.452 to 1.3

Line up the decimal points:     1.452
    + 1.3
       
"Pad" with zeros:     1.452
    + 1.300
       
Add:     1.452
    + 1.300
      2.752

Example: Add 3.25, 0.075 and 5

Line up the decimal points:     3.25
      0.075
    + 5.
       
"Pad" with zeros:     3.250
      0.075
    + 5.000
       
Add:     3.250
      0.075
    + 5.000
      8.325

That's all there is to it: line up the decimal points, pad with zeros, then add normally.

Subtracting

To subtract, follow the same method: line up the decimal points, then subtract.

Example: What is 7.368 − 1.15 ?

Line up the decimal points:     7.368
    1.15
       
"Pad" with zeros:     7.368
    1.150
       
Subtract:     7.368
    1.150
      6.218

To check we can add the answer to the number subtracted:

Example: Check that 7.368 minus 1.15 equals 6.218

Let us try adding 6.218 to 1.15

Line up the decimal points:     6.218
    + 1.15
       
"Pad" with zeros:     6.218
    + 1.150
       
Add:     6.218
    + 1.150
      7.368

It matches the number we started with, so it checks out.

 

Putting In Zeros

Why can we put in extra zeros?

A zero is really saying "there is no value at this decimal place".

  • In a number like 10, the zero is saying "no ones"
  • In a number like 2.50 the zero is saying "no hundredths"

So it is safe to take a number like 2.5 and make it 2.50 or 2.500 etc

But DON'T take 2.5 and make it 20.5, that is plain wrong.

 

958, 959, 1336, 1337, 3455, 3456, 3457, 3458