The Math Forum

Search All of the Math Forum:

Views expressed in these public forums are not endorsed by NCTM or The Math Forum.

Math Forum » Discussions » Education » math-teach

Notice: We are no longer accepting new posts, but the forums will continue to be readable.

Topic: Alien IQ Test
Replies: 12   Last Post: Jun 7, 2000 2:33 PM

Advanced Search

Back to Topic List Back to Topic List Jump to Tree View Jump to Tree View   Messages: [ Previous | Next ]
Ted Alper

Posts: 118
Registered: 12/6/04
Re: Alien IQ Test
Posted: Jun 6, 2000 1:37 AM
  Click to see the message monospaced in plain text Plain Text   Click to reply to this topic Reply

The problem doesn't say what it means to crack
the bone "at random", but if we assume this means
the break is made from a uniform distribution along the
length of the bone, then I think the answer is that
the average ratio is infinite.

we can assume the bone is of length 1
and we can use symmetry to reduce the problem to a break chosen
uniformly on (0,1/2) (it doesn't matter whether the longer piece
is on the right or the left)

then if x is that point in the interval (0,1/2) where the
break occurs, the ratio of the longer side to the shorter side is:

so the AVERAGE value of this ratio is...
the integral (1-x)/x dx from 0 to 1/2.

but this integral plainly diverges (heck, (1-x)/x will be greater
than 0.5/x and the integral of THAT diverges...

So if you believe the uniform distribution is what is meant by cracking
the bone "at random", then the answer is that the average ratio
of the lengths is infinite, in the sense that as you do the experiment
repeatedly, you'd expect the average ratio to grow without bound.

Ted Alper

Point your RSS reader here for a feed of the latest messages in this topic.

[Privacy Policy] [Terms of Use]

© The Math Forum at NCTM 1994-2018. All Rights Reserved.