Cool Math/Logic Problem

Bill Murphy · #1 01-28-2005, 05:07 AM

Gotta stocking stuffer book of math problems for XMas. Had just glanced it over but then I saw this one. It was composed by Sam Loyd, a very famous 19th century puzzle & chess master.

What I like about it is there's a eureka moment that has nothing to do w/setting up multi-variable equations, or esoteric knowledge. Not real tough, but fun. Here goes.

Two ferrys travel across a river all day. The two piers are directly across from each other, and the ferrys always leave at exactly the same time and keep constant speeds.

On one trip they pass each other 720 yards from Pier A. On the trip back they pass each other 400 yards from Pier B. How wide is the river?

Alobar · #2 01-28-2005, 05:12 AM

this answer seems to be easy to be correct, but heres what I got in white below

1120

Bill Murphy · #3 01-28-2005, 05:14 AM

Nope. [img]/images/graemlins/wink.gif[/img]

Alobar · #4 01-28-2005, 05:15 AM

[ QUOTE ]
Nope. [img]/images/graemlins/wink.gif[/img]

[/ QUOTE ]

lol, I knew that couldnt be right...oh well [img]/images/graemlins/frown.gif[/img]

daryn · #5 01-28-2005, 05:29 AM

do the speeds of each boat ever change?

in other words we have ferry 1 and ferry 2. say ferry 1 travels at speed X, ferry 2 travels at speed Y.

does ferry 1 always travel at X? does ferry 2 always travel at Y? of course they don't have to from the wording, but i'm asking.

if they DO always go at the same speed, then the problem makes no sense and has no solution.

if they DON'T, then the problem has an infinite number of solutions.

Skjonne · #6 01-28-2005, 05:38 AM

Solution in white:

 1440

daryn · #7 01-28-2005, 05:40 AM

<blockquote>In risposta di:<hr />
Solution in white:

 1440 

[/ QUOTE ]

logic please

pshreck · #8 01-28-2005, 05:42 AM

[ QUOTE ]
[ QUOTE ]
Solution in white:

 1440 

[/ QUOTE ]

logic please

[/ QUOTE ]

Wait to see if that is the right answer first.

Bill Murphy · #9 01-28-2005, 05:43 AM

I prolly shoulda just copied the problem word for word from the book, but its not that complicated. Yes, for these two trips Ferry1 is traveling at a constant speed X and Ferry2 at constant speed Y, but that's not the key to it. It's not a per se math problem.

daryn · #10 01-28-2005, 05:44 AM

<blockquote>In risposta di:<hr />
<blockquote>In risposta di:<hr />
<blockquote>In risposta di:<hr />
Solution in white:

 1440 

[/ QUOTE ]

logic please

[/ QUOTE ]

Wait to see if that is the right answer first.

[/ QUOTE ]

does it matter if he is right? he used some sort of logic to arrive at an answer.