MacRumors Forums Can anyone get this tricky math problem?
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Feb 9, 2008, 05:53 PM   #76
CalBoy
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Join Date: May 2007
Quote:
 Originally Posted by JML42691 There are two known ways to make \$1.00 out of 50 coins, what are they? Assuming that we are using American currency: \$.01 \$.05 \$.10 \$.25 \$.50
Do we have to use precisely 50 coins?
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 Feb 9, 2008, 06:00 PM #77 psychofreak Retired   Join Date: May 2006 Location: London Can someone spot what this pattern is, and in doing so find what starting (numbers) have a finite sequence: 1: 1, 11, 21, 1112, 3112, 211213, 312213, 212223... 2: 2, 12, 1112, 3112... 3: 3, 13, 1113, 3113, 2113, 211213... 4: 4, 14, 1114, 3114, 211314, 31121314, 41122314, 31221324... 0
Feb 9, 2008, 06:02 PM   #78
swiftaw
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Quote:
 Originally Posted by JML42691 There are two known ways to make \$1.00 out of 50 coins, what are they? Assuming that we are using American currency: \$.01 \$.05 \$.10 \$.25 \$.50
2*\$0.10, 8*\$0.05, 40*\$0.01
1*\$0.25, 2*\$0.10, 2*\$0.05, 45*\$0.01
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Feb 9, 2008, 06:07 PM   #79
swiftaw
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Location: Omaha, NE, USA
Quote:
 Originally Posted by psychofreak Can someone spot what this pattern is, and in doing so find what starting (numbers) have a finite sequence: 1: 1, 11, 21, 1112, 3112, 211213, 312213, 212223... 2: 2, 12, 1112, 3112... 3: 3, 13, 1113, 3113, 2113, 211213... 4: 4, 14, 1114, 3114, 211314, 31121314, 41122314, 31221324...
It's verbal. Each term is gotten by 'reading' the previous term.

For example, the top sequence starts with a 1 (or one 1), so the next term is 11, that is read as two 1's so the next term is 21, that is read as one 1, one 2, or 1112, and so on.

Edit: There seems to be a typo in sequence 3
3: 3, 13, 1113, 3113, 2123, 112213...

Edit2: None of the sequences are finite, but the sequence starting at 22 will just be 22,22,22,22,22,...

Last edited by swiftaw; Feb 9, 2008 at 06:17 PM.
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Feb 9, 2008, 06:19 PM   #80
JML42691
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Quote:
 Originally Posted by CalBoy Do we have to use precisely 50 coins?
Yes, but now it has been solved, I figured that it would take people a little longer than that.
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 Feb 9, 2008, 06:20 PM #81 Nermal Moderator     Join Date: Dec 2002 Location: Whakatane, New Zealand How do you make 1000 by adding eight 8s? 0
Feb 9, 2008, 06:22 PM   #82
CalBoy
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Join Date: May 2007
Quote:
 Originally Posted by Nermal How do you make 1000 by adding eight 8s?

Can we perform any operations other than adding?
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Feb 9, 2008, 06:22 PM   #83
swiftaw
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Quote:
 Originally Posted by Nermal How do you make 1000 by adding eight 8s?
888+88+8+8+8
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Feb 9, 2008, 06:23 PM   #84
CalBoy
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Quote:
 Originally Posted by swiftaw 888+88+8+8+8
Something leads me to believe you've heard of a few of these before.
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Feb 9, 2008, 06:24 PM   #85
swiftaw
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Quote:
 Originally Posted by CalBoy Something leads me to believe you've heard of a few of these before.
Actually, no, I'm just pretty good with numbers
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Feb 9, 2008, 06:26 PM   #86
CalBoy
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Join Date: May 2007
Quote:
 Originally Posted by swiftaw Actually, no, I'm just pretty good with numbers
Well that explains that!

See I suck horribly at them.
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 Feb 9, 2008, 06:33 PM #87 penter macrumors 6502a     Join Date: Jun 2006 so do you want the spreadsheet back, with my name?? __________________ jaded fanboy 0
 Feb 9, 2008, 06:42 PM #88 xlii macrumors 68000     Join Date: Sep 2006 Location: Millis, Massachusetts Just going back to the original cat problem in post #1. The question says the girls are on the bus and the backpacks are on the bus and the big cats are in the backpacks so they are also on the bus... BUT... It doesn't say where the little cats are... so... it is just as valid to assume that the little cats are not on the bus so you do not count their legs... 0
Feb 9, 2008, 07:02 PM   #89
Frisco
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Quote:
 Originally Posted by xlii Just going back to the original cat problem in post #1. The question says the girls are on the bus and the backpacks are on the bus and the big cats are in the backpacks so they are also on the bus... BUT... It doesn't say where the little cats are... so... it is just as valid to assume that the little cats are not on the bus so you do not count their legs...
Finally someone who was confused like myself. Makes me feel like less of an idiot now.

At least I got this great thread started with some very interesting math problems.
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Feb 9, 2008, 07:04 PM   #90
jsw
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Quote:
 Originally Posted by xlii It doesn't say where the little cats are... so... it is just as valid to assume that the little cats are not on the bus so you do not count their legs...
It also doesn't mention how many boys, adults, centipedes, or pianos are in the bus, so, yes, it's poorly specified.
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Feb 9, 2008, 08:33 PM   #91
EricNau
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Location: San Francisco, CA
Quote:
 Originally Posted by jsw It also doesn't mention how many boys, adults, centipedes, or pianos are in the bus, so, yes, it's poorly specified.
I'm still trying to figure out who's driving the bus, and how many legs they may (or may not) have.
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Feb 9, 2008, 09:57 PM   #92
penter
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Join Date: Jun 2006
Quote:
 Originally Posted by xlii Just going back to the original cat problem in post #1. The question says the girls are on the bus and the backpacks are on the bus and the big cats are in the backpacks so they are also on the bus... BUT... It doesn't say where the little cats are... so... it is just as valid to assume that the little cats are not on the bus so you do not count their legs...
lol just work out the problem however you can, and try inputting it into the spreadsheet's password. you'll get it eventually, i'm sure. it wasnt that hard lol

Now i just want to know if the spreadsheet should be uploaded after imputting my name, or something...
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Feb 9, 2008, 10:20 PM   #93
Baron58
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Join Date: Feb 2004
Quote:
 Originally Posted by CalBoy Ok, since you asked. There are 3 doors. Behind 1 door lies immense wealth and riches. Behind the other two lie certain death. A guard asks you to choose a door and you pick #2. The guard then reveals to you what's behind Door #1 and you see that behind it was one of two chances of certain death. The guard now asks you if you would like to change your selection from Door #2 to Door #3. Mathematically is there a probability increase that benefits you if you change doors? BTW, I don't know the answer to this, but I've seen it thrown around a few times
Yes. You're always better off switching.
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 Feb 9, 2008, 10:22 PM #94 twistedlegato macrumors 65816     Join Date: Jun 2006 This one stumped me for a long time. I felt so stupid when i realized how easy it was. "You are a bus driver. At your 1st stop you pick up 20 people. At your 2nd you drop off 10 and pick up 13. At your 3rd stop you drop off 11 and pick up 24. And at your 4th stop you pick drop off 7 people and pick up 9. What colour are the bus driver's eyes?" __________________ Out of the Frying Pan, into the Fire 0
Feb 9, 2008, 10:24 PM   #95
EricNau
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Join Date: Apr 2005
Location: San Francisco, CA
Quote:
 Originally Posted by twistedlegato This one stumped me for a long time. I felt so stupid when i realized how easy it was. "You are a bus driver. At your 1st stop you pick up 20 people. At your 2nd you drop off 10 and pick up 13. At your 3rd stop you drop off 11 and pick up 24. And at your 4th stop you pick drop off 7 people and pick up 9. What colour are the bus driver's eyes?"
Blue.

...That's a classic, although every time I've heard it, it ended with "How old is the bus driver?".
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Feb 9, 2008, 10:25 PM   #96
Doctor Q

Join Date: Sep 2002
Location: Los Angeles blood donor center
Quote:
 Originally Posted by jsw It also doesn't mention how many boys, adults, centipedes, or pianos are in the bus, so, yes, it's poorly specified.
A bus has stopped and the driver and all passengers, pets, and other living creatures have gotten off, except that one centipede remains on the floor under a seat. On top of the same seat is a take-out food carton, in which a passenger accidentally left a turkey leg and a lucky rabbit's foot.

How many legs are on the bus?
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Feb 9, 2008, 11:02 PM   #97
swiftaw
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Join Date: Jan 2005
Location: Omaha, NE, USA
Quote:
 Originally Posted by CalBoy Ok, since you asked. There are 3 doors. Behind 1 door lies immense wealth and riches. Behind the other two lie certain death. A guard asks you to choose a door and you pick #2. The guard then reveals to you what's behind Door #1 and you see that behind it was one of two chances of certain death. The guard now asks you if you would like to change your selection from Door #2 to Door #3. Mathematically is there a probability increase that benefits you if you change doors? BTW, I don't know the answer to this, but I've seen it thrown around a few times
This is a classic problem known as the Monty Hall problem. It is a classic example in conditional probability. If you don't switch the probability of winning is 1/3, if you do switch it is 2/3, so you should always switch.
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Feb 9, 2008, 11:09 PM   #98
jsw
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Join Date: Mar 2004
Location: Andover, MA
Quote:
 Originally Posted by Doctor Q A bus has stopped and the driver and all passengers, pets, and other living creatures have gotten off, except that one centipede remains on the floor under a seat. On top of the same seat is a take-out food carton, in which a passenger accidentally left a turkey leg and a lucky rabbit's foot. How many legs are on the bus?
The problem remains insufficiently specified, as centipedes - assuming non-mutant ones with all of their legs - have between 30 (the typical number) and 354 legs. We at least need to know the species.

And there was no mention of the occurrence or lack thereof of non-biological legs.
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Feb 9, 2008, 11:19 PM   #99
Doctor Q

Join Date: Sep 2002
Location: Los Angeles blood donor center
Quote:
 Originally Posted by jsw The problem remains insufficiently specified.
That is the correct answer. But you should have waited for somebody else to say 101, so we could tease them for not knowing their entomology.

There could also be legs on the bus seats, but we'll ignore that.
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 Feb 9, 2008, 11:26 PM #100 queshy macrumors 68040     Join Date: Apr 2005 is the answer to the OPs problem 10990? 0

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