perplexus.info :: Just Math : Formula None Racer

Formula None Racer (Posted on 2003-10-03)

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?

Submitted by Ravi Raja

Rating: 2.6000 (10 votes)

Solution: (Hide)

45 mph
Let the two digit number be represented by 10x+y.
After one hour, the milestone shows the number 10y+x.
The distance traveled so far is: (10y+x) – (10x+y) = 9(y – x)
After another hour, the milestone shows 100x+y.
The distance traveled in the second hour is:
(100x+y) – (10y+x) = 9(11x – y).
Then, we have:
9(11x – y) = 9(y – x)
This gives y = 6x.
Since x and y are both digits, x must be 1 and y must be 6.
Therefore, the milestones mentioned read: 16, 61 and 106.
Now, since the car traveled 45 miles each hour, it is clear that the speed of the car is 45 mph.

Comments: ( You must be logged in to post comments.)

Subject	Author	Date
Puzzle Solution (Method II)	K Sengupta	2008-02-15 10:55:11
Puzzle Solution (Method II)	K Sengupta	2008-02-14 13:51:15
Puzzle Solution (Method I)	K Sengupta	2008-02-14 13:48:33
answer	K Sengupta	2008-02-13 11:45:50
puzzle	pardhasaradhi	2006-06-19 14:16:02
infosys puzzles	pardhasaradhi	2006-06-19 14:08:09
Infosys puzzzles	pardhasaradhi	2006-06-19 14:03:51
Infosys puzzzles	pardhasaradhi	2006-06-19 14:01:50
Question	K Sengupta	2005-07-05 06:07:10
90 miles, two hours, simple!	humfoozneydannle	2004-12-31 18:29:52
The driver is a moron	Jack Squat	2004-01-21 16:49:44
re: Solution	Howard Bandy	2003-11-01 11:08:38
Solution	Howard Bandy	2003-11-01 11:07:14
re(3): Divisibility	SilverKnight	2003-10-10 16:49:34
re(2): Divisibility	Nick Hobson	2003-10-10 16:40:52
re: Divisibility	SilverKnight	2003-10-10 16:29:47
Divisibility	Nick Hobson	2003-10-10 16:20:38
Solution	DrBob	2003-10-09 17:25:07
solution	amber	2003-10-09 02:44:54
solution	Ruxi	2003-10-06 15:00:05
Ans ...	priyank	2003-10-06 08:49:57
re: solution	mohan	2003-10-06 02:46:15
solution	Freddy Grants	2003-10-05 01:35:12
re: No Subject	SilverKnight	2003-10-03 14:26:48
No Subject	tim	2003-10-03 14:22:04
re: Well, since fwaff was expecting one.	fwaff	2003-10-03 11:33:06
re(2): please ignore	SilverKnight	2003-10-03 11:27:05
re: Well, since fwaff was expecting one.	SilverKnight	2003-10-03 11:22:38
Well, since fwaff was expecting one.	Charlie	2003-10-03 11:21:10
solution	Lee	2003-10-03 11:20:15
re: please ignore	fwaff	2003-10-03 10:55:39
please ignore	FatBoy	2003-10-03 10:12:57
re: Solution - no brute force	SilverKnight	2003-10-03 09:51:30
Solution - no brute force	fwaff	2003-10-03 08:42:30
solution	SilverKnight	2003-10-03 08:20:11

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