Subtracting large numbers

Now we are going to look at subtracting large numbers. Let’s try 85695 – 3862. Again, we line up the ones, tens, hundreds, etc.

We put a minus sign (−) between the two numbers.

We start with the ones

Then we move onto the tens

Then it’s the hundreds

Here we have to do 6 − 8 but 6 − 8 = -2. We can take 1 from the thousands column to solve this problem

Here’s how:

Our number 85695 is made up of 8 * 10000 + 5 * 1000 + 6 * 100 + 9 * 10 + 5 * 1.

This is the same as 8 * 10000 + 4 * 1000 + 16 * 100 + 9 * 10 + 5

Notice that there is 1 less 1000 (4 instead of 5) and 10 more 100s (16 instead of 6) and 1000 = 10 * 100 so the two numbers are equal.

You can see in the images below that 85695 can be constructed in both of these ways

So, going back to our subtraction:

We can take a 1 from the thousands column and place a 10 in the hundreds columns so we have 4 thousands and 16 hundreds.

Now we can do the subtraction to produce a positive number

And then finish off the subtraction

85695 – 3862 = 81833