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#1 2007-01-11 03:20:50

soha
Real Member
Registered: 2006-07-07
Posts: 2,530

Help

I AM NOT ABLE TO UNDERSTAND THIS PROBLEM
PLEASE HELP ME

IF THE SUM OF n TERMS OF A PROGRESSION IS 

FIND THE 10 th TERM OF AN A.P
dunno
also how to write fractions here

Last edited by soha (2007-01-11 04:16:50)


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#2 2007-01-11 03:43:27

luca-deltodesco
Member
Registered: 2006-05-05
Posts: 1,470

Re: Help

im not quite sure what thats mean to mean, but, if you mean writing fractions as in LaTeX. then itd be

Last edited by luca-deltodesco (2007-01-11 03:43:38)


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#3 2007-01-11 03:51:31

soha
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Registered: 2006-07-07
Posts: 2,530

Re: Help

Ok.got It .edited My Post Above.
Now How To Write Raise To Like;- 3² In Fractions


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#4 2007-01-11 04:09:45

luca-deltodesco
Member
Registered: 2006-05-05
Posts: 1,470

Re: Help

 a^b, a^{ba}, a^{b+a}

in general, if you only need to use a single symbol, you dont need the {}

 \frac{a^b}{a^{2+\frac{1}{2}}}


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#5 2007-01-11 04:17:48

soha
Real Member
Registered: 2006-07-07
Posts: 2,530

Re: Help

thanks.i used it in my above post.well does anyone know the answer of my  question


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#6 2007-01-11 04:26:28

ewojmath
Member
Registered: 2007-01-11
Posts: 1

Re: Help

Alexi’s wallet contains four $1 bills, three $5 bills, and one $10 bill. If
Alexi randomly removes two bills without replacement, determine
whether the probability that the bills will total $15 is greater than the
probability that the bills will total $2.

the answer to the question was
P(15) = 6/56
P(2) =12/56
Are these answers right? If they are, how did they get that?

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#7 2007-01-11 04:32:43

luca-deltodesco
Member
Registered: 2006-05-05
Posts: 1,470

Re: Help

why did you post this in this thread? delete youre post and put it in a new thread please, or someone move it if they have the designated power.


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#8 2007-01-11 05:20:50

mathsyperson
Moderator
Registered: 2005-06-22
Posts: 4,900

Re: Help

Luca's right, you shouldn't ask questions in another person's topic. Unfortunately, mods don't have the power to move single posts to another topic like I'd need to here. The best thing I could do would be to delete this post and create another topic with that question pasted in.

Or I could just attempt to resolve both questions right now and we wouldn't have a problem anymore. smile

To Soha:

If I've interpreted your question correctly, then you're given the formula for the sum of the first n terms of a sequence, and from that you need to find the formula for each single term. This will be easier if we break it up.

From triangular numbers, we know that the sum of the first n terms in a sequence where the nth term is n is given by n(n+1)/2, or

.

This is kind of similar to the formula you have. There are 3 n²'s in your formula, so if we change it to have 3 n's as well then we will have 3 of the triangular number formulas.

To change the n into 3n, we added 2n, so we now need to take away 2n as well. There is a 2 on both sides of the fraction, so they cancel and leave just -n.

For the sum of the first n terms in a sequence to be -n, that means that each individual term in the sequence would have to be -1. And so combining this with the 3n that we already found, we get that the nth term in your sequence is given by 3n-1.

Hopefully you understand all that, I don't think I've explained it overly well. Once you've got this bit, finding the 10th term is easy. 3*10-1 = 29.

---

To ewojmath:

The answers are correct. $15 needs to be made up of $5 and $10. There are 3 $5 bills and just one $10 bill, so there are 3 ways of drawing a $5 and then a $10 bill. But there are also 3 ways of drawing a $10 bill and then a $5 bill, so this makes 6 ways in total.

There are 8 ways of drawing any bill from the wallet, and then for each of those there are 7 ways of drawing out another bill after that. So there are 8*7 = 56 combinations in total that could happen. We've already found that 6 of these lead to a total of $15, so the probability is 6/56.

For $2, Alexi needs to pick a $1 bill both times. In the first draw, there are 4 ways of doing this because there are 4 $1 bills in her wallet. The second time, there are only 3 ways because one of the bills will have already been removed. So this means that in total there are 4*3 = 12 ways of drawing out $2 with 2 bills. As we already know that the total amount of combinations is 56, this means that the probability is 12/56.

Therefore, she is more likely to draw out $2 than $15.


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#9 2007-01-11 20:54:45

soha
Real Member
Registered: 2006-07-07
Posts: 2,530

Re: Help

sorry.i cannot understand it.
please explain briefly


"Let us realize that: the privilege to work is a gift, the power to work is a blessing, the love of work is success!" smile smile
- David O. McKay

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#10 2007-01-11 23:56:06

mathsyperson
Moderator
Registered: 2005-06-22
Posts: 4,900

Re: Help

You are given that

, and you want to find out what f(i) is.

From triangular numbers, we know that

. We also know that
, because that is a trivial result.

So if we can write your expression in terms of (n²+n)/2's and n's, then we can find f(i).

This means that

, and so
.


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