4 1/3-1 1/4
Write them vertically like this
4 1/3
-1 1/4
Get the LCD of 3 and 4. Since they have no common
factors other than 1, the LCD is their product, 12.
To start, we need to change the 1/3 to something
over 12.
Notice that the denominator of 1/3, which is 3,
needs to be multiplied by 4 to become 12. So
multiply both the denominator and numerator by 4.
That gives you a numerator of 4 and a denominator
of 12. So put an equal sign after 4 1/3 and put
4 4/12 after it, like this
4 1/3 = 4 4/12
-1 1/4
Now we need to change 1/4 to something over 12.
Notice that the denominator of 1/4, which is 4,
needs to be multiplied by 3 to become 12. So
multiply both the denominator and numerator by 3.
That gives you a numerator of 3 and a denominator
of 12. So put an equal sign after -1 1/4 and put
1 3/12 after it, like this
4 1/3 = 4 4/12
-1 1/4 = -1 3/12
Now we draw a line underneath like this
4 1/3 = 4 4/12
-1 1/4 = -1 3/12
---------
Now we subtract the whole parts: 4 - 1 = 3
and we subtract only the numerators of the
fractions, 4-1, getting a numerator of 3,
keeping the denominator of 12, like this:
4 1/3 = 4 4/12
-1 1/4 = -1 3/12
---------
3 1/12
When the numerator of the top fraction is
smaller than numerator of the bottom
fraction, you have to do something else,
but that wasn't required here.
Edwin
