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?

(let the milestones be at ab, ba, a0b)
The distance by inspection is 90a (diff' between 1st and 3rd)
So average speed = 90a/2 mph
ba-ab=45a (halfway point) [ba = 10b + a, also, ab = 10a + b]
9(b-a)=45a
b=6a
only a=1, b=6 work
Av. speed = 45mph
(milestones at 16 61 106)

Posted by Lee on 2003-10-03 11:20:15