# Maths problem

help me as my brain has gone to mush...

21 to 40 of 72 messages
Stump    pirate
03/04/2008 at 11:48
The cow problem
03/04/2008 at 11:52

That's what I said!

03/04/2008 at 11:52
wow
03/04/2008 at 12:25
I'm disappointed.  Did I say what side of the fence the cow was on?
Stump    pirate
03/04/2008 at 12:27
It' doesn't matter if you do the problem in 4 dimensional space
03/04/2008 at 12:43

8 + 4 - 9 x 3 = 24

or am I too late!

I have a circular field (well paddock pen) and I have horse  ..... I am sorely tempted to go outside and try rope thing at lunchtime

03/04/2008 at 12:50
TP have you checked that?
03/04/2008 at 12:52

9-8=1

4-1=3

3*8=24

yes?

Garr    pirate
03/04/2008 at 13:08

Ah shoot!  I read the question wrong.

I got  = [(r^2)/2]^(-1/2)

but that's if you tie the cow to the centre of the field.  I admit I couldn't work it out if I'd read the question properly.  I'm lame with Sin, Cos and Tan.

Garr    pirate
03/04/2008 at 13:09
Can RW put on a function that allows all threads with 'maths problem' in the title, cause an email to be sent to me?  I do love this kind of stuff, though to be fair, the first question was a bit easy (though if you're brain doesn't follow the right paths, you can get stuck on things like that for ages).
Stump    pirate
03/04/2008 at 13:16
Garr the soln to the cow problem is on my link further up the page
iron fraggle    pirate
03/04/2008 at 13:23

Garr - yes I know the first one was a bit easy!  My excuse is that my boys have very kindly given me their cold and my head is full of goo

(plus, these being the not so  bright members of the class, I was looking for really easy solutions, so having to do several steps to get to 3x8 is a bit difficult for them!)

03/04/2008 at 13:36

8 + 4 - 9 x 3 = 24   should of course have read 8 + 4 - 9 x 8 = 24

Thank  you Barkles.  I will now write out 100 times 'I must not forum without my glasses on'

Do I have to see you after school for punishment too?

Garr    pirate
03/04/2008 at 13:49

Thanks Stump.  I knew I got it wrong only when I saw the answer.

Fraggle, don't worry, I wasn't saying you should've got it.  There are plenty of times I should've got things but my brain just let's me down at the last moment.  I'll never forget getting 99% in a calculus test because I managed to add 7 and 6 together to get 15!!  If you start looking in the wrong direction with something like that question, you might spend days trying to get the answer.

Do we know the problem below (which I'm not going to name because it'll be too easy for people to pull out the solution)?  It's always a cracker to share with people.

The "XXXXX XXXX" problem

Imagine you're in a game.  There are 3 doors in front of you which you cannot see behind.  There is only you and the quiz host in this game.

Behind 2 doors are coconuts, and behind 1 door is a luxury yacht (they're big doors, ok?).  Now, we'll assume you always want the luxury yacht, just in case there's anyone out there with a bizarre coconut fetish!

You are asked to pick a door.

The quiz host now removes one of the other doors (but he will never take away the luxury yacht because that'd be a pretty naff game).

You are then told you can either stick with the door you have chosen, or you can change to the other door.  Remember, you still can't see what's behind either one.

What should you do?
Should you stick, change, or does it make naff all difference either way?
What are the probabilities each way?

NB - this is a question often used to show how straight forward logic can get the wrong answer and unpleasant, but well formulated maths will prevail, BUT if you are careful with your logic, you'll get it right.

Stump    pirate
03/04/2008 at 13:55
Barbarella
mellifera    pirate
03/04/2008 at 13:56

I know that one Garr - I was about to post the same problem myself. It's a great example.

TP - that's still not right unless you write (8 + 4 - 9)  x 8 = 24

8 + 4 - 9 x 8 =  is 8 + 4 - 72 = -60

left to right associativity is only true for operators of the same precedence.

mellifera    pirate
03/04/2008 at 13:58

here's another I like because it shows that our gut feeling on conincidence is often wrong

All twenty-five of my students want to invite me to their birthday party. What is the probability that I get at least two invites for the same day?

It's a lot higher than you would guess.

Edited: 03/04/2008 at 13:59
03/04/2008 at 13:59
ah - the Monty Hall problem

choose a different door
mellifera    pirate
03/04/2008 at 14:00
for MH probability goes from 1/3 to 1/2 if you change
03/04/2008 at 14:01

Been a long time since I was at school but don't think you do need the brackets.  If you follow the sum along the line and key it into a calculator as it stands the number at the end is 24.

left to right associativity is only true for operators of the same precedence - Sorry, I have no idea what this means - not only been a long time since school but I was never very good at arithmetic .... that's why I'm an accountant

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