# Elevators

#### mathmaniac

##### Active member
5 people are on the 17th,19th,20th,26th and 31st floors.We have to get all of them out.
But the elevator doors open only when all of them are between the 21st and 25th.
There are 2 buttons,+8 and - 13,that will be activated only when 2 elevators are selected.The building has in total 49 floors.
How will you get all of them out?

#### Unknown008

##### Member
Do you mean that none of the 5 people can be saved?

I'm asking because 'the elevator doors open only when all of them are between the 21st and 25th' which is not satisfied at the start and hence can never be satisfied if there are no means to change floors besides using the elevators. Unless they can use the staircases, which leads to 'they can all use the stairs to get out of the building' as the lazy answer.

#### mathmaniac

##### Active member
Do you mean that none of the 5 people can be saved?
All 5 can be saved out.

I'm asking because 'the elevator doors open only when all of them are between the 21st and 25th'
Note:between 21 and 25 includes 21 and 25 too(otherwise only 3 will get out).This is a flash game and I just copied the instructions but they wrote it wrong.

Sorry.

which is not satisfied at the start
Yes.

and hence can never be satisfied
No.

if there are no means to change floors besides using the elevators.
Who said?You forgot the +8 and -13 buttons?

Unless they can use the staircases, which leads to 'they can all use the stairs to get out of the building' as the lazy answer.
I assure you this one has a mysterious answer rather than a lazy answer.

And let me know is there anyway to show you the game...

And see <link removed by moderator> for further clarification.

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#### MarkFL

Staff member
...

And see <removed link> for further clarification.
mathmaniac,

You really should not send our members to other forums to read posts you have made to others regarding the problems you have posted here as well as on other sites. You should address the issues directly for our members here as well, even if this simply means copying and pasting the relevant information.

Better yet would be to include the questions others have asked at the other site, and your responses to these questions

You should keep in mind what is easier for everyone else (the many), rather than what is easier for you (the few).

When you post a challenge question here, you should be prepared to offer clarification if requested, and this clarification should be given here if possible. Now if you are linking to an article then a link is okay, but simply linking to a topic on another forum should be avoided. You should also be prepared before you post the problem with a clearly explained solution that you have verified is correct.

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#### Unknown008

##### Member
We agree that:

But the elevator doors open only when all of them are between the 21st and 25th
And

which is not satisfied at the start
Yes.
Since the elevator doors open only when everyone is between the 21st floor and the 25th inclusive, the elevator doors will never open for anyone on the other floors. Otherwise, the first statement is contradicted.

It no more matters whether there are buttons in the elevator or not, the elevators just won't open by what you are saying.

#### mathmaniac

##### Active member
Ok,here is the game.

See it for yourself.

I don't wanna waste many words here.

#### MarkFL

Staff member
...

I don't wanna waste many words here.
What do you mean by this? Providing an explanation for what you mean is not wasting words, is it?

#### mathmaniac

##### Active member
I mean Unknown008 always says it is impossible.

And now that I have shown the game,words are less worthy.

#### MarkFL

Staff member
It is fine, and even instructive to show the game, but you should also try to address the points made as clearly as you can. During this discussion you will learn. A lot of learning can come simply from expressing what you know to others.

#### Unknown008

##### Member
Well, there was one important detail you left out: the 5 people are locked into the elevators.

My set up of moves:
+ indicates +8 floors
- indicates -13 floors

Hence:
+ = +8
- = -13
++ = +16
-- = -26
+- = -5
++- = +3

Code:
Minimum moves:       1      2      3      3       4
Current floor:      17     26     20     19      31
Combination:         +     +-    ++-    ++-    ++--
Requirements:    +4:+8  -1:-5  +1:+5  +2:+6  -6:-10
Final floor:        25     21     23     22      21
Total + = 8
Total - = 5

Since the elevators work in pairs, we need another - in there. Possible combination would be to add one "++-" to either the ones on floor 21, or the one on floor 22. I choose the one on floor 21, so it becomes:

Code:
Minimum moves:       1      5      3      3       4
Current floor:      17     27     20     19      31
Combination:         +  +-++-    ++-    ++-    ++--
Requirements:    +4:+8  -1:-5  +1:+5  +2:+6  -6:-10
Final floor:        25     24     23     22      21
Total + = 10
Total - = 6

Even numbers this should work.

Actually, I tried it and it does work.