Math Is Fun Forum

Steph.nyc

Guest

Word Problems: Multiplying Fractions

Hi,

I'm working on some fraction word problems and I understand that if the problem contains certain keywords like "of" you need to multiply. However, my question is - why can't you divide? When reading the problem it leads you to think that you need to divide and I'm trying to understand this.

EX: A recipe for banana oat muffin calls for 3/4 of old fashioned oats. You are making 1/2 the recipe. How much oat should you use?

If you are making only half, wouldn't you divide the 3/4? (Yes, I know "of" tells you to multiply). Sort of like if you had 4 cookies and are giving half away, wouldn't you divide to know how many you are giving away?

Thanks in advance for your help.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Word Problems: Multiplying Fractions

Hi;

You can divide by 2 or multiply by 1 / 2. Welcome to the forum.

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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.

numquester

Member

Registered: 2016-12-12

Posts: 19

Re: Word Problems: Multiplying Fractions

Obviously, you want 1/2 of 3/4 of old fashioned oats for making 1/2 of the recipe.  Maybe what it isn't so obvious is that division by 2 gives the same result as multiplication by 1/2: 

To make sense of the above, remember that any number can be rewritten as the number over 1...

...and to get half of something, we have to divide it by 2...

...which can be rewritten as a multiplication...

And so...

Last edited by numquester (2017-01-17 04:04:41)