1. ## Algebraic Fractions

Hi All,

Can someone tell me why:

2a/3b x 6/a2b = 4/ab2

Why does 6 become 4? Is this to do with cancelling common factors?

This is why I dislike the book Engineering Mathematics by Stroud for this very reason. It will give you some really basic example to start with then ask you to solve an equation when they haven't explained the specifics properly.

Thanks

2. ## Re: Algebraic Fractions

Originally Posted by mc444
Hi All,

Can someone tell me why:

2a/3b x 6/a2b = 4/ab2

Why does 6 become 4? Is this to do with cancelling common factors?

This is why I dislike the book Engineering Mathematics by Stroud for this very reason. It will give you some really basic example to start with then ask you to solve an equation when they haven't explained the specifics properly.

Thanks

$\dfrac{2a}{3b} \cdot \dfrac{6}{a^2b} = \dfrac{2a \cdot 6}{3b \cdot a^2b} = \dfrac{2a \cdot 2 \cdot 3}{3b \cdot a \cdot ab} = \dfrac{2\cancel{a} \cdot 2 \cdot \cancel{3}}{\cancel{3}b \cdot \cancel{a} \cdot ab} = \dfrac{4}{ab^2}$

3. ## Re: Algebraic Fractions

Skeeter you legend. Thanks for that. This has cleared a lot of confusion up!

4. ## Re: Algebraic Fractions

Equivalently, 2* 6= 12 and 12/3= 4.

5. ## Re: Algebraic Fractions

Originally Posted by mc444
Hi All,

Can someone tell me why:

2a/3b x 6/a2b = 4/ab2

Why does 6 become 4? Is this to do with cancelling common factors?

Oh, those sides are equal, but not why you think they are. When you write/type them out horizontally,
place grouping symbols around these needed denominators as such:

2a/(3b) x 6/(a2b) = 4/(ab2)