Math Is Fun Forum
You are not logged in.
- Topics: Active | Unanswered
#1 2016-02-10 10:46:07
- anna_gg
- Member
- Registered: 2012-01-10
- Posts: 232
Skippy the kangaroo
Skippy the kangaroo is standing 7 meters away from his feeder bowl and wants to reach it. It can jump one or more jumps ahead and each jump can be of one or two meters long, and also one jump backwards, which is one meter long. Skippy can reach its bowl by a sequence of one or more jumps ahead and only one jump backwards, but not the first one. In how many different ways can Skippy reach its bowl (consider the bowl as a point without dimensions and also that it must arrive exactly at the edge of the bowl without bypassing it - as if it is placed in front of a wall)?
Last edited by anna_gg (2016-02-11 07:47:02)
Offline
#2 2016-02-10 11:23:31
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Skippy the kangaroo
Hi;
Do you mean in the sequence of jumps forward he must take 1 and only 1 backward jump?
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
Offline
#3 2016-02-10 18:34:36
- anna_gg
- Member
- Registered: 2012-01-10
- Posts: 232
Re: Skippy the kangaroo
Right, and this cannot be the first jump (i.e. Skippy cannot start by jumping backwards). I also did a correction in the wording, to explain that it cannot jump past to the bowl and then return with a backward jump; it must arrive exactly to the bowl with a forward jump (the last one).
Last edited by anna_gg (2016-02-11 07:50:13)
Offline
#4 2016-02-11 12:57:38
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Skippy the kangaroo
So, if he has travelled 6 meters meaning he is 1 meter from the bowl he can not jump 2 meters forward?
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
Offline
#5 2016-02-11 16:02:01
- Relentless
- Member
- Registered: 2015-12-15
- Posts: 631
Re: Skippy the kangaroo
Yes, that is implied in the last sentence. Also, the very first jump must be forwards
Offline
#6 2016-02-11 19:03:51
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Skippy the kangaroo
Hi;
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
Offline
#7 2016-02-11 19:37:16
- phrontister
- Real Member
- From: The Land of Tomorrow
- Registered: 2009-07-12
- Posts: 4,880
Re: Skippy the kangaroo
Hi Anna;
Last edited by phrontister (2016-02-11 20:52:11)
"The good news about computers is that they do what you tell them to do. The bad news is that they do what you tell them to do." - Ted Nelson
Offline
#10 2016-02-12 12:01:59
- anna_gg
- Member
- Registered: 2012-01-10
- Posts: 232
Re: Skippy the kangaroo
Why did you change your mind? I also got 167.
Sorry, change of mind.
Offline
#11 2016-02-12 12:44:36
- phrontister
- Real Member
- From: The Land of Tomorrow
- Registered: 2009-07-12
- Posts: 4,880
Re: Skippy the kangaroo
Hi;
Last edited by phrontister (2017-02-26 22:08:55)
"The good news about computers is that they do what you tell them to do. The bad news is that they do what you tell them to do." - Ted Nelson
Offline
#12 2016-02-12 14:51:01
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Skippy the kangaroo
Thanks for the M code, I did it another way and had some extra answers.
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
Offline
#13 2016-02-12 14:56:02
- phrontister
- Real Member
- From: The Land of Tomorrow
- Registered: 2009-07-12
- Posts: 4,880
Re: Skippy the kangaroo
How did you do it? Do you think all your answers are valid?
"The good news about computers is that they do what you tell them to do. The bad news is that they do what you tell them to do." - Ted Nelson
Offline
#14 2016-02-12 14:57:16
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Skippy the kangaroo
I scratched the code because I knew some of the answers were wrong!
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
Offline
#15 2016-02-12 15:09:31
- phrontister
- Real Member
- From: The Land of Tomorrow
- Registered: 2009-07-12
- Posts: 4,880
Re: Skippy the kangaroo
Oh.
Anna got the same answer as mine and Nehushtan's first answer.
"The good news about computers is that they do what you tell them to do. The bad news is that they do what you tell them to do." - Ted Nelson
Offline
#16 2016-02-12 15:13:00
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Skippy the kangaroo
I did not doubt that 167 was correct. I just knew 180 was not.
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
Offline
#17 2016-02-12 15:26:19
- anonimnystefy
- Real Member
- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,049
Re: Skippy the kangaroo
I will have to agree on 167.
Last edited by anonimnystefy (2016-02-12 15:36:25)
Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.
Offline
#18 2016-02-12 15:28:15
- phrontister
- Real Member
- From: The Land of Tomorrow
- Registered: 2009-07-12
- Posts: 4,880
Re: Skippy the kangaroo
I like Nehushtan's logic, but he left something out in both answers and included something in the first that gave the correct answer there.
"The good news about computers is that they do what you tell them to do. The bad news is that they do what you tell them to do." - Ted Nelson
Offline
#19 2016-02-12 15:34:10
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Skippy the kangaroo
A's code is nice though.
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
Offline
#20 2016-02-12 15:36:04
- phrontister
- Real Member
- From: The Land of Tomorrow
- Registered: 2009-07-12
- Posts: 4,880
Re: Skippy the kangaroo
That's very tight, stefy! 
Not that I understand it...too advanced for me.
I had tried to tighten mine because of all the repeats, but couldn't see how.
"The good news about computers is that they do what you tell them to do. The bad news is that they do what you tell them to do." - Ted Nelson
Offline
#21 2016-02-12 15:36:54
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Skippy the kangaroo
But you used the same idea...
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
Offline
#22 2016-02-12 15:37:13
- phrontister
- Real Member
- From: The Land of Tomorrow
- Registered: 2009-07-12
- Posts: 4,880
Re: Skippy the kangaroo
A's code is nice though.
What do you mean?
"The good news about computers is that they do what you tell them to do. The bad news is that they do what you tell them to do." - Ted Nelson
Offline
#23 2016-02-12 15:38:42
- phrontister
- Real Member
- From: The Land of Tomorrow
- Registered: 2009-07-12
- Posts: 4,880
Re: Skippy the kangaroo
Did you mean "A" for stefy? I thought you meant Anna.
"The good news about computers is that they do what you tell them to do. The bad news is that they do what you tell them to do." - Ted Nelson
Offline
#24 2016-02-12 15:40:15
- phrontister
- Real Member
- From: The Land of Tomorrow
- Registered: 2009-07-12
- Posts: 4,880
Re: Skippy the kangaroo
Gotta have some lunch...catch you later.
"The good news about computers is that they do what you tell them to do. The bad news is that they do what you tell them to do." - Ted Nelson
Offline
#25 2016-02-12 15:42:12
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Skippy the kangaroo
I meant anonimnystefy's code. You both used partitions.
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
Offline