How to Subtract Mixed Numbers With Different Denominators

Transcript

Hi, I'm Charlie Kasov, and this is how to subtract mixed numbers with different denominators. Now, it's very easy to subtract mixed numbers with different denominators as long as you first turn them into improper fractions. So for example if we have 2 and 3/5ths, we want to subtract 1 and 3/4ths, first we have to turn both of these phrases into improper fractions. So 2 and 3/5ths, well, 2 is equal to 10 divided by 5 and 3/5ths so we now have 13/5, 1 is equal to 4/4 and if we add in 3/4 we get 7/4. Now we need to do 13/5 minus 7/4. The next step is finding the lowest common denominator for both and it looks like both of these go into 20. So we're going to turn this into 20ths by multiplying by 4/4 and 13 times 4 is 52 over 20 and we're going to multiply this by 5/5 because that gives us 20ths. So that's 34/20. So now 52 minus 35 is going to be 17/20. And because 17 is prime this fraction is irreducible but that is how you can subtract mixed numbers with different denominators.

Charlie Kasov has been tutoring high school mathematics since 2004. He is qualified to teach several math subjects, including geometry, algebra, trigonometry and probability.