Solve the Decimal Subtraction: 18 - 16.31 in Vertical Format

In order to avoid confusion in solving the exercise, we will first add two zeros to the number 18 as follows:

$18.00\\-16.31\\$

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

Subtract the hundreds after the decimal point:

$0-1=$

Given that we are unable to solve the exercise, we will borrow ten from the tens digit of the whole number before the decimal point (since the tenths digit after the decimal point is also 0)

Now the tens digit of the whole number before the decimal point will become 7 and the tenths digit after the decimal point will change from 0 to 10

We will then proceed to borrow ten from the tenths digit after the decimal point and it will change from 10 to 9 and the hundreds digit will change from 0 to 10

We can now solve the exercise.

Subtract the hundreds after the decimal point:

$10-1=9$

Subtract the tenths after the decimal point:

$9-3=6$

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

$8-1-6=1$

$1-1=0$

And we get:

$18.00\\-16.31\\01.69$

We can ignore the zero before the 1 and therefore we obtain the number: 1.69