Now on to the numerator. This is where the method gets its name.
Draw a line connecting the denominator of our second fraction to the numerator of our first fraction.
In this we get a line connecting 2 and 1. We then like the denominator multiply the two numbers and we get 2.This gives us the first half of our cross.
Now for the second
Same procedure except this time we will start by using the other denominator. So we end up with a line going from 6 to 1. Again we multiply the two numbers and we get 6.
Now we combine each cross we got for our numerator with the operation we are using in this case edition.
So we well have
2+6/12
The 2 from the first cross and the 6 from the second.
Simply to 8/12
then reduce and we get
2/3.
You can use this method for subtraction and addition. It is important to do have the first cross be the one from the right hand denominator to the left hand numerator. When adding addition it wont matter, but in subtraction it will, because if done the other way around it will give you the wrong sign. So its just good habit to do it properly no matter the operation. Fool-proof method (if arithmetic is done correctly) for doing fractions without having to find a common denominator. However, you will mostly have to reduce it.