Young Writers Society

Snoink, I need you now!
*clutches chest and staggers around*
I'm not even going to say what percentage I got in Math this semester..but suffice to say that it was completely abysmal.

Anyways. Umm...I know I learnt Cross Multiplying in 4th grade or something, but I can't...seem to remember it...heh heh. So yeah. I majorly need to get help with Cross multiplication, else I fail the upcoming Math mini-exam.



Please? *is meek*

I can help ^_^

Let's say you had 2/4=x/8. When you cross multiply in this example, you'd multiply the two and the eight and set it equal to the 4 multiplied by the x:

2*8=x*4

or

16=4x

where you'd then solve for x and come up with four. (see scribble below for a better representation)

Now you might have something different than x. Maybe you have 2x+2, in which case you'd do the same thing if the equation is 2/4=(2x+2)/8. You'd multiply the top of one by the bottom of the other and set it equal to the bottom of one by the top of the other:

2*8=4*(2x+2)

which simplifies to:

16=8x+8

8=8x

and finally

x=1

I have NO idea what kind of depth your math teacher goes into, but I wrote up something for you that we teach the undergrads here, so yay? Basically, it's how to set up a proportion (you might know this already) and then how to solve it algebraically and THEN how to cross multiply. Because, once again, I have no idea how your teacher wants you to do problems.

Here we go again...

Because we love unit conversions!

And remember, opposites are stuck together, just like a magnet, but the two guys who are like each other want to be near each other... sort of. That's why the cm is across from the cm.

Solving it algebraically.

And yeah, I know some people who can't understand cross multiplication but can do algebra quite fine, so I'm showing you these both ways, just to cover all bases. Too much knowledge is never a bad thing, right!

And yes, PLEASE notice the equal sign in between them. I've found CALCULUS students, for goodness sakes, decide that they were going to do cross-multiplication without the equal sign in there, and it doesn't work. At all.

If you don't see an equal sign in between them, then treat it as normal multiplication. DO NOT cross multiply!

And then... the magic.

I find that colors can sometimes make things apparent to me, so hopefully it's that way for you too. Sometimes, black and white doesn't work. So I put green and blue in, to imply what gets multiplied. Hopefully, it makes sense...?

Solving it:

Oh golly, that looks so complicated! I never did anything like that... is it an American "thing"? *is very very hopeful*

Hope your grade goes well, Elfie!

Well, I've never even heard of cross multiplication, nor have I ever seen anything like that. I'm guessing, like Twitters, that it's an American thing.

*Strides [s]ignorantly[/s] confidently onwards*

I've done it before. Apparently you only need it in England if you take maths and further maths at A level and then you spend a lesson or two on it and start applying it to partial fractions and other fun areas of maths.

I'm an American and the two schools I went to NEVER taught that!
Confusing! =]

Wow, thanks you guys!
I really appreciate it! I'm pretty sure I know what I'm doing now. ^_^
And Snoink, you saved my life. I shudder to think what my parents would do if I failed another test...*shudders*
Anyways, muchos gracias (that how you spell it? Lol) for the time and brain power you put into helping me!
Thanks again,
Ayra

Wow... I haven't learnt that yet. My school is for dummies. I feel stupid