Re: Just for fun, making 100
- From: "abeaujean@xxxxxxxxxxxxx" <abeaujean@xxxxxxxxxxxxx>
- Date: 3 Jul 2006 07:35:34 -0700
abeaujean@xxxxxxxxxxxxx a écrit :
Not precisely the goal of this group, but I can't resist the idea. It
was so much fun looking at professional engineers scratching their
heads for minutes and hours trying to solve the following simple
problem.
I looks like a homework but it is not.
How can one arrive at a result of 100, using the five numbers 1 7 7 7 7
only once each and basic arithmetic operations (+ - * / ).
Actually very simple believe me, and non engineer minded people are the
faster to the solution, which is very interesting in how much thinking
is distorted by one's personal experience and scholarship.
Have fun.
OK. Good to see that the solution to the problem has been found.
Let me tell you a few things.
The first time the problem was posed in my company (employing around 10
engineers), it was voluntarily posed only to the engineers and in a
rather vague way, just the way I did it here, the target being to give
food for thoughts and leave any solution open.
Then came out at first that fast solution: 177 - 77, but the guy who
launched the fun then restricted the scope by saying "No, no
concatenating".
Then, everybody started some basic arithmetic playing around, with
results always nearing 100 but never reaching the exact number.
In parallel (for those more systematic and programmatic) a few tried
the software way, trying all possible combinations (which turned out
here to be unsuccessful).
Also came out some very exotic ways (including macros in Excel files
and such unbelievable things that I forgot).
Then, the same guy who launched the thing came in again and said "No,
the solution is very simple. Try again".
And, since I am a hardware engineer and do not have the expertise to
write the program and hate too complicated things, I decided to try
just by thinking.
And the rationale was then (7 + 7) * 7 = ? . Well that is 98. How many
missing ? 100 - 98 = 2. How to make 2 with the remaining 7 and 1 ?. By
dividing 14 by 7 .... (YEAHHH).
And that makes the (7 + 7) * (7+1/7).
The problem by itself is interesting. But it is at least as interesting
to watch how people get to the solution as finding the solution itself,
and also all the discussions that the problem leads to.
And that is what I mean when I say that common, non technical people
(and there is obviously no contempt whatever in my mouth neither for
the common nor for the technical people) generally arrive to the
solution faster because they tend to use common sense and simple
thinking rather than algorithmic machinery that they know nothing
about.
So, as I said (and all that is so pretty obvious):
-- People try to solve with the tools they have, the grocer or
housewife tries to solve with a calculator and a pencil, the engineer
being more biased to using high level tools shall try to use them, even
if he(she) also has a lot of common sense and basic konwledge.
So, good fun I hope for all, and a short but interesting look at man's
behaviour.
.
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