Expert: Lynn Houston - 3/26/2009

Question
how would you explain how to add 1/5 2/3 and 5/6


Answer
First, you have to find the lowest common denominator.  That means the lowest number that all of the 3 denominators will go into equally.  That is going to be 30 (5*6, 3*10 and 6*5).  Now that you know the common denominator, you have to change all the fractions into 30ths.  To do that, you multiply each fraction by x/x, where x is the number that it takes to make each denominator 30.  For example for 1/5, you'd multiply by 6/6, 2/3 * 10/10 and 5/6 * 5/5.  Those equal

6/30 + 20/30 + 25/30 =

Once all the denominators are the same, you just add (or it's the same for subtraction) all the numerators together, so

6/30 + 20/30 + 25/30 = 51/30  That reduces to 1 21/30 = 1 7/10