A car is travelling at a uniform speed.
The driver sees a milestone showing a 2-digit number. After travelling for an hour the driver sees another milestone with the same digits in reverse order. After another hour the driver sees another milestone containing the same two digits as in the first one but the two digits separated by a zero(0).

What is the speed of the car?

(In reply to Solution - no brute force by fwaff)

I didn't brute force either! :-)

(Of course, I didn't really explain it, to be fair)

But basically, very easy thought process:
if the first two milestones are two digit, and the third is three digit... the third must be in the 100-199 range... (in fact we can narrow it down further, but...) the point is the first digit must be 1.

so we have:

1b
b1
10b

clearly the b must be in the center (between 1 and 10)... so possible cases must be 5 or 6 (or thereabouts)...

very straightforward... all in the head.... no brute force... ;-)

Posted by SilverKnight on 2003-10-03 09:51:30