Subtract Decimals: Find 39.2 - 13.421 with Proper Alignment

In order to avoid confusion whilst solving the exercise, add two zeros to the number 39.2 as follows:

$39.200\\-13.421\\$

Now let's proceed solve the exercise in the correct order:

Subtract the thousands after the decimal point:

$0-1=$

Given that we cannot subtract, we will instead borrow ten from the tenths digit after the decimal point (note that the hundreds digit is 0 therefore we cannot borrow from there)

After borrowing ten from the tenths digit, the hundreds digit will become 10 and from it we'll borrow ten to solve our exercise.

The hundreds digit will become 9 and we'll get the exercise:

$10-1=9$

Let's subtract the hundreds after the decimal point:

$9-2=7$

Let's subtract the tenths after the decimal point, remembering that we borrowed ten from it:

$2-1-4=1-4$

Due to the fact that we cannot subtract, we will instead borrow ten from the tens digit of the whole number as shown below:

$11-4=7$

Finally, let's subtract the whole numbers before the decimal point accordingly:

Remember that we borrowed ten from the tens digit, therefore:

$9-1-3=5$

$3-1=2$

We should obtain the following result:

$39.200\\-13.421\\25.779$