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pseries: Newbie | Next Rank: 10 Posts; Posts: 2; Joined: Fri Aug 09, 2013 5:39 am

by pseries » Fri Aug 09, 2013 5:57 am

Hello All Members,

I am beginning my preparations for the GMAT. It has been a while I studied maths so plz don't mind if I ask a question that is too simple for you.

I was going through fractions and I got confused with fraction addition.

If we were to add simple fractions 3/8 + 3/10 we multiply 3 x 5 / 40 + 3 x 4 / 40 i.e. multiply numerator and denominator by the same number so that denominator is the same.

but if we want to add 1 / 4 + 3 / 6 we cross multiply. ie. 1x6 + 3x4 / 24

Someone please explain me. Apologies for the simple question!

Source: Beat The GMAT — Problem Solving | Fri Aug 09, 2013 5:57 am

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by [email protected] » Fri Aug 09, 2013 6:22 pm

Hi pseries,

The rules of math stay the same, regardless of what the numbers (or variables) are.

When adding (or subtracting) fractions, you need a common denominator:

With your first example:

3/8 + 3/10 has a common denominator of 40 (although you could use 80 and reduce the result later), so you need to convert both fractions:

3(5)/8(5) + 3(4)/10(4)

15/40 + 12/40 = 27/40

With your second example:

1/4 + 3/6 has a common denominator of 12 (you could also use 24 and reduce later), so convert the fractions:

1(3)/4(3) + 3(2)/6(2)

3/12 + 6/12 = 9/12 = 3/4

As you learn (or relearn) more and more math, you have to memorize the concept, then be prepared to use it in ways that are other than obvious (such as with variables, exponents, radicals, etc.).

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