Spider Man
Vote Conservative
Premium
join:2002-12-11
Thornhill, ON
| Math help please :)
Books at harry discount bookstall sell for 14 dollars, or 19 dollars. The store has 70 more of the 19$ boosk then then 14$ books. If the average price of all the books is 17 dollars, how much books are there?
this one is a toughy for me pls dont laugh  ;) |
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spaterson
Premium
join:2001-09-02
Gloucester, ON | 210 $19 books
140 $14 books
350 books total. |
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Spider Man
Vote Conservative
Premium
join:2002-12-11
Thornhill, ON | reply to Spider Man
thanks alot, how did you do that. |
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LaZ3R
Premium
join:2003-01-17
 ·Rogers Hi-Speed
1 edit | reply to Spider Man
Hmm... Odd, that was a question on the page we got for homework today LOL :)
What school do you go to? :o
Let x = # of $14 books
Let y = # of $19 books
your two equations should be something like this:
x+70=y
14x+19y=17
-------
x+y
Basically 14x+19y(Divided by x+y)=17
And you just substitute from there.
You can also just multiply (x+y) if you move it over to the other side so you'd get: 14x+19y=17(x+y) which is easier to work with :)
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Life is a game of blackjack. You keep playing until you bust. |
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spaterson
Premium
join:2001-09-02
Gloucester, ON
·Rogers Hi-Speed
| reply to Spider Man
said by Spider Man  :thanks alot, how did you do that. You don't wanna know.
I've been out of school way too long to rememeber the x and y's. I was horrible at math back then too. Looks like LaZ3R's equations are on the right track though. |
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m0x
I love juice too
Premium
join:2002-11-04
San Francisco, CA
| reply to Spider Man
Now, let's say I take 5 books randomly, without putting them back. What are the chances that I have at most 2 19$ books in the 5 I took?
Well, my chances of of getting a 19$ in one pick is (210/350) = 0.6
So my probability of getting a 14$ one is 1-0.6 = 0.4
There are 6 different outcome. I can get:
0 19$ books 5 14$ books
1 19$ books 4 14$ books
2 19$ books 3 14$ books
3 19$ books 2 14$ books
4 19$ books 1 14$ books
5 19$ books 0 14$ books
So I have to add up the probability of getting a 0, 1 and 2 books together to get at most 2 19$ books.
The formula for the probability is:
p(x) = ( 5! / (x!*((5-x)!)) ) * 0.6^x * 0.4^(5-x)
where x is the number or 19$ book you'll get.
So we'll add up p(0), p(1) and p(2)
That'll make: p(0) + p(1) + p(2) = 0.01024 + 0.0768 + 0.2304
The probability of getting at most 2 19$ books randomly from 5 books taken from your store is thus: 31.744%
Please accept my apology. People already answered the question and I've been studying non-stop the past days on my stats class. This is a very simple example. Stats are cool, go in science kids.
Oh, and I probably made a mistake or two.
--
Just because you're paranoid doesn't mean they're not out to get you |
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Spider Man
Vote Conservative
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join:2002-12-11
Thornhill, ON | reply to Spider Man
ty once again guys |
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Mr
Premium
join:2002-12-25
clubs: 
| reply to LaZ3R
said by LaZ3R :Hmm... Odd, that was a question on the page we got for homework today LOL :) What school do you go to? :o Let x = # of $14 books Let y = # of $19 books your two equations should be something like this: x+70=y
14x+19y=17
-------
x+y Basically 14x+19y(Divided by x+y)=17 And you just substitute from there. You can also just multiply (x+y) if you move it over to the other side so you'd get: 14x+19y=17(x+y) which is easier to work with :) I honestly hope your being sarcastic about what school he goes to .... |
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dirtyjeffer
Lest We Forget
Premium
join:2002-02-21
London, ON
·Rogers Hi-Speed
| reply to Spider Man
said by Spider Man :If the average price of all the books is 17 dollars, how much books are there? hmmmm...three things.
1). when the hell are you ever going to need to do this in real life...this is one thing i always hated about the math problems...they were always useless...they should stick with teaching people how to give correct change first.
2). i know its a math class, but it doesn't mean english shouldn't be important too...it should be "How many books are there?";)
3) for the answer to the quiz, i would do what EVERY business owner would do...either look up the inventory on the computer system, or simply count them during a physical inventory.
sorry, while i was always good at math in school, i found it stupid as most of the things that were taught were useless.
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"The only thing more greedy than a corporation, are its customers." |
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Bender2000
Bite My Shiny Metal Ass
Premium
join:2002-05-06
Roxboro, QC
clubs: | the actual problem is useless from the perspective of books, etc, however the problem teaches the person how to perform remedial algebra, which is useful in some areas of real life. |
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Wolfie00
My dog is an elitist
Premium
join:2005-03-12
| reply to dirtyjeffer
said by dirtyjeffer :1). when the hell are you ever going to need to do this in real life...this is one thing i always hated about the math problems...they were always useless...they should stick with teaching people how to give correct change first. ... 3) for the answer to the quiz, i would do what EVERY business owner would do...either look up the inventory on the computer system, or simply count them during a physical inventory. sorry, while i was always good at math in school, i found it stupid as most of the things that were taught were useless. There's a good discussion of this phenomenon on Slashdot under a posting called Intelligence in the Internet Age
I thought this little contribution was insightful:
Smart people will use technology to augment their intelligence. Dumb people will use it to become lazier. And in between there will be mixes of augmentation and lazy reliance. I don't think there's a single answer to this question. I think this has always been true, but technology amplifies this gap.
Different occupations do require different skills, but I would have to say everyone should be capable of something this basic, because it does keep coming up in real life; in your example it may not come up every day for the business owner, but it sure as hell comes up for the guy that builds the computer system. But the business owner himself needs to have some basic capabilities -- what if he, as I did some time ago, sets out to build a fairly elaborate deck. I quickly discovered there was a fair amount of math involved because it was, basically, a sort of mini-engineering project. I see this kind of problem as an exercise in the basic reasoning and planning capabilities that most of us need, if not all the time, then certainly once in a while.
And both spaterson's answer and lazer's equations are right. They're simultaneous equations so you substitute (x+70) for y in the second equation to reduce it to one variable and then solve it. The brute force method would play out like this:
14x + 19(x+70)
------------------ = 17
x+(x+70)
33x + 1330
-------------- = 17
2x+70
33x + 1330 = 17(2x+70)
33x + 1330 = 34x + 1190
34x = 33x + 140
x = 140
and since y = x+70, y = 210 and spaterson wins the yellow Porsche 911s
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deadmeat
Premium
join:2003-03-21
Sonoma, CA | reply to Spider Man
The answer is 42. |
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noelstrom
meh.
Premium
join:2003-04-07
London, ON | reply to Spider Man
When in doubt, pick c. |
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m0x
I love juice too
Premium
join:2002-11-04
San Francisco, CA
| reply to dirtyjeffer
said by dirtyjeffer :i know its a math class, but it doesn't mean english shouldn't be important too...it should be "How many books are there?";) Did you lose your shift key somewhere dj? 
Seriously, maths are very good at developping the mind. It's not about "when am I ever going to have to use this in my life?" (which, by the way, can be said about most things learned in school) but rather about "what am I learning doing this?"
This is a very simple example of a linear equation system with 2 equations and 2 variables. I can tell you right away that I need to resolve linear equation system almost on a daily basis. It is the very basis of mechanic for example, and it's the reason the roof is not falling on your head.
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Just because you're paranoid doesn't mean they're not out to get you |
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Tikker_LoS
join:2004-04-29
Regina, SK
 ·SaskTel Saskatchewan
| reply to dirtyjeffer
said by dirtyjeffer :said by Spider Man :If the average price of all the books is 17 dollars, how much books are there? hmmmm...three things. 1). when the hell are you ever going to need to do this in real life...this is one thing i always hated about the math problems...they were always useless...they should stick with teaching people how to give correct change first. I actually do stuff like this all the time in my job(manage capacity for IP networks) |
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Serbtastic
You Know How Many People I Have Buried?
Premium
join:2002-02-24
Stoney Creek
| reply to dirtyjeffer
said by dirtyjeffer :they should stick with teaching people how to give correct change first. I was at Lick's last week grabbing some lunch, and the girl at the counter rang up my total on the register. The amount was $8.04, so I handed her a $10 bill, and went fishing for change. She rang in the $10 and the cash drawer opened. I found a dime and gave it to her, and she was totally stunned. Spent a good 2 minutes trying to calculate the difference in her head. Finally I told her she owed me $2.06 change.
Kids today! |
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mr weather
Premium
join:2002-02-27
Mississauga, ON | Yep, that's happened to me on more than one occasion.
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"It's all coming down!!" - Mike Holmes |
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angelalways
Life Lessons Learned
Premium
join:2003-11-27
Cloud*17
1 edit | reply to Spider Man
After reading this thread, I need an Advil. |
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AR
Premium,ExMod 2001-04
join:2000-09-21
Toronto, ON
·Rogers Hi-Speed
| reply to Serbtastic
It's the same as spelling. We use calculators and spell checkers. I notice myself using the calculator a lot. And who needs mental arithmetic when you have calculators in your PDA, your cell, your PC.
--
The Confederacy was an Ownership Society. |
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Clipper
join:2002-05-23
Stoney Creek, ON
| reply to Serbtastic
said by Serbtastic :I was at Lick's last week grabbing some lunch, and the girl at the counter rang up my total on the register. The amount was $8.04, so I handed her a $10 bill, and went fishing for change. She rang in the $10 and the cash drawer opened. I found a dime and gave it to her, and she was totally stunned. Spent a good 2 minutes trying to calculate the difference in her head. Finally I told her she owed me $2.06 change. The thing alot of younger people didn't get a chance to do growing up was learning tricks to make stuff like that easier. While i'm only 25, my dad taught me alot of stuff that made doing math in my head easier,stuff they dont' teach in school. I can almost guarentee that the cashier in your example trying to re-do the math of 10.10 - 8.04 to figure out your change, whereas people that don't rely on calculators would know its alot easier to take the change the register gave on 10.00 and just add $0.10 to it. |
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