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GARCIE Grandmaster Cheater Reputation: 1
Joined: 16 Nov 2006 Posts: 566

Posted: Tue Jul 06, 2010 5:14 pm Post subject: Hello RS; mind helping me with my math? 


Here's the question
"The number of bacteria in a culture quadruples every 15 hours. How many times more bacteria are there after 30 hours than there are after 20 hours?"
This question is related to the logs section of Math 12 (BC curriculum)
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Fatchile How do I cheat? Reputation: 6
Joined: 30 May 2006 Posts: 0

Posted: Tue Jul 06, 2010 5:20 pm Post subject: 


40 TIMES? I mean.... 10x4=40. Forgive me if I answered wrong.
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Nirojan How do I cheat? Reputation: 108
Joined: 16 Sep 2008 Posts: 0 Location: seshville

Posted: Tue Jul 06, 2010 5:23 pm Post subject: 


what if somehow it quadruples AT the 15 hour mark?
is it just multiplying by 2 twice spreadout throuwait no
huh
this is confusing
WHY MATH IN THE SUMMER ANYWAYS?
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Yazu™ How do I cheat? Reputation: 14
Joined: 24 Oct 2008 Posts: 0

Posted: Tue Jul 06, 2010 5:29 pm Post subject: 


2/3's more?


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gogodr I post too much Reputation: 125
Joined: 19 Dec 2006 Posts: 2050

Posted: Tue Jul 06, 2010 5:33 pm Post subject: 


x is the number of bacteria
it goes at a reason of 4x / 15 hours
so the total at time 30h should be x * 4 / 15 * 30 which is 8x
total at time 20h should be x * 4 / 15 * 20 which is (16/3)x
the reason in between them both.
How many times more bacteria are there after 30 hours than there are after 20 hours?
should be
8x / [( 16/3)x]
which is 3/2
at 30h you have 1.5 times the bacteria you had at 20h
thats your answer


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Anarchy Expert Cheater Reputation: 29
Joined: 15 Feb 2009 Posts: 104 Location: There.

Posted: Tue Jul 06, 2010 5:44 pm Post subject: 


gogodr wrote:  x is the number of bacteria
it goes at a reason of 4x / 15 hours
so the total at time 30h should be x * 4 / 15 * 30 which is 8x
total at time 20h should be x * 4 / 15 * 20 which is (16/3)x
the reason in between them both.
How many times more bacteria are there after 30 hours than there are after 20 hours?
should be
8x / [( 16/3)x]
which is 3/2
at 30h you have 1.5 times the bacteria you had at 20h
thats your answer  gogodragon and his dragon intelligence.


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GARCIE Grandmaster Cheater Reputation: 1
Joined: 16 Nov 2006 Posts: 566

Posted: Tue Jul 06, 2010 5:47 pm Post subject: 


kk i got it, it's not 1.5 times greater, thanks gogodr though, you set me on the right track
the answer is 2.5 times greater
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