Use this shortcut to subtract fractions from whole numbers.
The shortcut even works with mixed fractions

Transcript
Welcome to MooMooMath where we upload a new Math video everyday.
In this video I would like to show you an easy method for subtracting fractions from whole numbers.
To help, I would like to start with a story.
Imagine you are having pizza for dinner.
The pizza is cut into 8 equal slices.
Your little brother comes along, and eats one of the slices.
How many slices are left? yes 7
You can use this same concept to quickly subtract fractions from whole numbers.
I can write the original pizza as a fraction, 8/8 because any number over itself equals one
Your brother ate 1 slice, so I can write this as 1 over 8
Therefore 8/8 -1/8 = 7/8 because you only have 7 slices remaining from the original 8.
So now let’s apply this concept to subtracting fractions from whole numbers.
Let's go ahead and apply this concept for subtracting fractions from whole numbers.
Say we have 5 - 3/4
Here is the shortcut. First, subtract 1 from the whole number and that gives us 4.
Now we will rewrite the one as a fraction.
Remember, when we had the pizza divided into 8 slices, and we rewrote it as 8/8
What we will do is rewrite the one as a number over itself, and we will get the clue from the denominator of the fraction we are subtracting.
We will rewrite the one with the denominator over itself. The one will become 4/4
Lets rewrite this so it is not so messy.
5 -1 =4
Rewrite the one as 4/4
We got the clue from the denominator.
4/4 -3/4 = 1/4 and you can subtract because the denominators are the same.
So it becomes 4 1/4
Let's work a couple, and once you see three or four of these you will say, " This is really easy," and you can complete this in your head.
5 - 2/3
Subtract 1 from the 5 =4
I will rewrite the 1 as 3/3-2/3 = 1/3
Your answer is 4 1/3
Let's flip this over.
Rewrite a couple more.
Let's go with 8 - 9/19 This looks tricky, but it's not.
I subtract one from the 8=7
I get my clue from the denominator
I rewrite it as 16/16 -9/16 = 7/16
So I now have 7 7/16
Finally, the last one I will go with one kinda tricky
16-5/7
16-1 =15
Rewrite the one as a fraction and look at the denominator as a clue.
7/7-5/7 =2/7
Just subtract 7-5 = 2 and becomes 15 2/7
What is we have one like this.
8 - 2 4/7
How do we subtract this?
We have a whole minus a fraction. It is a mixed fraction, so here is my shortcut.
I will rewrite it into vertical fashion.
8-24/7
All I do is add one step.
8-2 =6 -4/7
Now I will work it the same as before.
Subtract one from six which equals five.
The 1 becomes 7/7 - 4/7 = 3/7 = 5 3/7

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