Evaluating expressions,

- anonymous

Evaluating expressions,

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- schrodinger

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- anonymous

Easiest problem ever, but I forgot how to do them,
|dw:1361117139126:dw|
Can someone show me step by step how to solve this or create a problem giving me an example? Thanks.!

- anonymous

\[1-\frac{ 694 }{ 896 }\] do you mean?

- anonymous

No, its P

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- anonymous

then p4 do you mean its power or 4 is multiplied?

- anonymous

like p4 or \[p^4\]

- anonymous

I have no idea... It just says 6P4,

- anonymous

Noo, its not that, I'll take a screenshot

- anonymous

ok... i am waiting for screenshot.

- anonymous

This is the problem,

##### 1 Attachment

- anonymous

this is Permutation.

- hartnn

ohh..its permutation!

- anonymous

I also have this problem that includes a exclamation mark, |dw:1361117585779:dw|
Do you know what its for?

- anonymous

& whats permutation? O_O
I have never ever heard of that

- hartnn

\(!\)
means a factorial.

- hartnn

\(n!= n(n-1)(n-2).......3.2.1\)
when n is a whole number.
like for example
5! = 5*4*3*2*1 = 120

- anonymous

answer is 1 it means that you need to expand 6 as 4 times and 8 as 6 times.

- anonymous

1/56

- hartnn

before getting to permutation, you should know what a factorial ! is .

- anonymous

OH.! so I had something like 10! I would have to do 10*9*8*7*6*5*4*3*2*1= etc..?

- hartnn

yes, thats correct.

- anonymous

6P4= 6*5*4*3
and
8P6= 8*7*6*5*4*3

- anonymous

yes you are correct.

- hartnn

do you want to know how to get that^ ?

- anonymous

I feel like I've done this stuff in 8th grade but had forgotten how to do some of this.
These questions are for my pre-cal class & I found it odd that I had a probability question in there

- anonymous

yes.

- hartnn

\(\huge ^nP_r = \dfrac{n!}{(n-r)!}\)

- anonymous

So basically I had to do the factorial (!) to the 6P & 8P?

- anonymous

yes.

- hartnn

\(\huge ^nP_r = \dfrac{n!}{(n-r)!} \\\huge ^6P_4 = \dfrac{6!}{(2)!} \\ \huge 8P_6 = \dfrac{8!}{(2)!}\)

- anonymous

Everything on the left side of the = is confusing to me

- hartnn

in the formula of nPr ?
its just a formula, so for 6P4, i plugged in n=6 and r=4 in the standard formula.

- anonymous

How would you know which ones to plug in?
Because in one you have 6P4 & in the next 8P6, I don't get how you go to that?

- hartnn

n is before P , r is after P .
in 6P4 , 6 is before P (so, n=6) and 4 is after P (so r=4)
does this makes sense ?

- anonymous

Ah, it does now.! :-)
Thanks you guys both for explaining this to me.!

- hartnn

Thank me when you get to correct answer.

- anonymous

What do you mean?

- hartnn

i meant to ask you, whether you could now figure out the answer of that question...

- anonymous

I do the factorial, 8*7*6*5*4*3*2*1, I thought?

- anonymous

& then divide my answer by 2?

- hartnn

thats for 8P2

- anonymous

Then I'm lost again,

- hartnn

i never said you are wrong. its just not the final answer.

- anonymous

Then I do the same with the 6

- hartnn

6P4 = 6*5*4*3
8P2= 8*7*6*5*4*3
Question asks, 1- 6P4/8P2 = 1- 6*5 / 8*7*6*5 = 1- 1/(8*7)
ok ?

- anonymous

Ah, I wasnt paying attention to the 1,

- anonymous

Would I have to subtract the 1 from the 6 & start factoring 5?

- hartnn

no...
first division operation is performed, so 6*5*4*3 will get cancelled from numerator and denominator, and what remains is just 1- 1/(8*7)
which i've already shown.

- anonymous

Thats confusing

- hartnn

ok, clear till this :
6P4 = 6*5*4*3
8P2= 8*7*6*5*4*3

- anonymous

Got that...

- hartnn

now divide them
6P4/8P2 =.... ?

- anonymous

I got 0.0178 etc...
Thats not right..

- hartnn

keep it in fractions..

- anonymous

I got 360 from 6*5*4*3 & 20160 from the factorial of 8.

- anonymous

How would I keep it in fractions?

- hartnn

you can also cancel out like this :
|dw:1361120576575:dw|
got that ?

- anonymous

Ah, got it.! I wasnt thinking about canceling out

- hartnn

ask if any more doubts.

- anonymous

What happened to the 4 & 2?

- hartnn

i just realized i mistyped 8P6 (and have written 8P2 instead)
4 and 2 where ?

- anonymous

The 4 after the P and the 2 after the other P

- hartnn

oh, we used the formula, right ?
6-4 = 2, so 2! in the denominator
8-6= 2, so 2! in the denominator

- anonymous

OH.! Ok I get it.!

- anonymous

1/56 wasnt correct, could it be 55/56 by any chance?

- hartnn

?? you forgot '1-...' again ?
1- 1/(7*8)= 1-1/56=(56-1)/56 = 55/56

- anonymous

*face palm*
Thank you.

- hartnn

welcome ^_^

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