On Wed, 20 Jan 2010 16:27:06 -0800, Darren New wrote:

> Jim Henderson wrote:
>> On Wed, 20 Jan 2010 08:11:28 -0800, Darren New wrote:
>> 
>>> Warp wrote:
>>>>   I have hard time parsing that question.
>>> It *is* messed up. The usual question is something like
>>>
>>> You have a race two miles long. For the first mile, one car goes 60MPH
>>> and the other goes 30MPH. How fast does the other car have to go to
>>> finish the race at the same time as the one going 60MPH?
>> 
>> Even then it doesn't parse correctly, because they've given you the
>> speeds for both cars - so asking how fast the slower car should go
>> doesn't make sense, because you've been told how fast it is going.
> 
> The race is two miles long. The slow car goes at a speed for one mile.
> What's the speed in the second mile?

That makes more sense - but fairly easy to answer algebraically.

> (I guess I left out that the fast car keeps going the same speed.)
> 
>> And I'm not sure that discarding the length of the track allows the
>> question to be answered even then.
> 
> No, that would eliminate the ability to answer.

How so?  If you know the distances and speeds, then the time at which 
both cars reaches the end of the distance becomes a solvable problem.

> Anyway, that's an easy question to answer. A slightly better version is
> this:
> 
> You want to average 60MPH over two minutes. You go 30MPH for the first
> mile. How fast do you have to go to average 60MPH for two minues?
> 
> Second alternate question: you want to average 60 MPH. You drive 10
> miles at 30MPH. How many miles do you need to drive at 90MPH to average
> 60MPH?

I agree, that question formulation would be easier to answer.

Jim

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