11/12 + (-23/28)

11/12 + (-23/28) =

 

11/12 - 23/28

 

When one subtracts (-) [ or adds (+) ] one fraction from another, one has to make common denominator (bottom).

Remember that the value of a fraction is retained when one multiply (*) or divide (:) the numerator (top) and the denominator (bottom) with the same number.

 

12 factorized is 2 * 2 * 3

28 factorized is 2 * 2 * 7 

 

We see that in order to get common denominator (bottom) one has to multiply the "12-fraction" by 7 and the "28-fraction" by 3:

 

$$\frac{11}{12}-\frac{23}{28}=
\frac{11*7}{12*7}-\frac{23*3}{28*3}=
\frac{77}{84}-\frac{69}{84}=\frac{8}{84}$$

 

Divide both the numerator and the denominator by 4:

 

8/84 = 2/21