Math Is Fun Forum

FrankBurhmont

Member

Registered: 2012-02-03

Posts: 2

Adding Algebraic Fractions

Hi,

I didn't really much pay attention to Fractions in school and am about go off to university. I think I have them pretty much down pat (Thanks to this site ) but am having trouble with an example from a textbook called "Understanding Year 8 Maths" by Warwick Marlin. I can't understand what he is doing with with Example 3 on Page 61 which is:
  6m + 4m
  10     5
= 6m + 8m
    10    10
= 14m
    10
= 7m
    5

It looks like what he is doing is cross multiplying and then dividing the numerator by the original denominator before finding the lowest common denominator.

But if he was doing that, then wouldn't the fraction on the left be 3m over 10? If not, then where did the 8m come from?

I thought that when adding fractions you needed to cross multiply the numerators with the denominators on the opposite sides and then find the lowest common denominator before adding the numerators?

Thanks for the help in advance!

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Adding Algebraic Fractions

Hi FrankBurhmont;

Welcome to the forum. Yes, when adding fractions you can use the cross multiplication method and you will get the right answer.

But that is not the only trick, here he is doing something else.

You are trying to get the denominators to be equal cause then all you have to do is add the numerators.

By multiplying the denominator of the fraction on the right by 2 you would get a 10. But if you multiply the denominator by 2 you must also multiply the numerator by 2.

Did you follow that?

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

FrankBurhmont

Member

Registered: 2012-02-03

Posts: 2

Re: Adding Algebraic Fractions

Wow, that's a cool trick Yes I did follow. That made perfect sense.

Thank you very much

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Adding Algebraic Fractions

Hi;

Your welcome but we can reduce that fraction to lowest terms.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.