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A group of four people has to cross a bridge .It is dark, and they have to light the path with a flashlight . No more than two people can cross the bridge simultaneously , and the group has only one flashlight . It takes different time for the people in the group to cross the bridge . Annie crosses the bridge in 1 minute, Bob crosses the bridge in 2 minutes, Cristy crosses the bridge in 5 minutes, Dorothy crosses the bride in 10 minutes. How can the group cross the bridge in 17 minutes?

I think Dorothy is the one who should be left behind. She's a liability.

Bob seems strong - can't he give Dorothy a piggyback ride?

**SPOILER**

This is my solution:

Annie & Bob cross; Bob stays, Annie returns. (total 3 minutes)

Cristy & Dorothy cross; they give the flashlight to Bob & he returns (total 12 mins)

Annie & Bob cross (2 mins)

= 17 minutes!I think you're right, Livelonger. But, it isn't stated that they need to hold the flashlight. What if they just laid the flashlight down at the head of the bridge to light it up, then everyone could easily cross without a problem. Total time: 15 minutes or less depending on the pairings.

** Spoiler II **

Here's my solution: Annie takes the flashlight, hits Bob, Cristy, and Dorothy in the head, pushes them each over the side of the bridge and then strolls across in about 5 minutes. It turns out Annie is a sociopath. This is an important fact that was somehow left out of the orignal description. She also keeps a goalie mask in her backpack.LOL

Why 17 minutes?

Do they have an appointment on the other side of the bridge or something?

That is the true question.

Answer me that and I'll give you a cookie.i think bothe livelonger and robin have given good suggestions but i'm gonna take robin's idea.

annie crosses the bridge and helps to light up thus making the way brighter. (1 min)

since bob is a guy,he can carry dorothy(assuming he can, grins) and cross but i'm gonna add some more time since dorothy seems to be more "afraid" you can say. so i would say he'd most likely take around 5-6 mins.(6 mins max)

after that, cristy will cross the bridge.(5 mins)

thus they'll more or less take 12-13 mins at the most.Best solution so far.

Do you have another homework question for us?

Riddle me this,

"You are a contestant on the game show Let's Make a Deal, and emcee Monty Hall has a game for you to play.

On stage are three huge doors, and he informs you that hidden behind one of the three doors is a brand new sports car, behind another is a donkey, and behind another is 400 pounds of bananas. (This may seem obvious, but your goal is to get the car, not the donkey or the bananas.)

He asks you to choose one door, and you will win the prize behind that door. You choose, but before he reveals what you have won, Monty reveals what's behind one of the doors you did not pick, and it's not the car. Before revealing what lies behind the remaining two doors, he makes you one final offer: if you wish, you may switch from your choice to the other remaining door.

The question is: Should you switch, should you not switch, or does it matter?"LOL that's from university course on the probabilistic theory. I don't remember neither the answer, nor the mathematics involved

It has been annoying me immensely. I believe it was originally connived by Vos Savant. I know the answer, but I still don't agree with it! I must have the IQ of a small rock.

My brain hurts just thinking about it and I know I'm not sleeping tonight until I have it worked out.

Thanks a lotlol, i need to read the ques again. probability question huh. hehehehe i used to kinda dislike tht topic during my high sch. hehehe well if one of the door he opened doesn't have car, then doesn't it mean tht there's a 50-50 chance of it being in yours?? if tht's the case, does switching or not really matter?? hmm unless it's like for example, the door tht didn't have was the first one. then maybe the car is in the sec one? i don know sometimes ppl like to put in alternate ways.

but in my opinion it all boils down to luck too so i would probably go with my choice and not switch.Dammit, this is still bugging me, but I am going with "It doesn't matter."

Solution;

http://nostalgia.wikipedia.org/wiki/Monty_Hall_problem

Just a little background note. Vos Savant is the person with the highest IQ living today.I am still not getting it. Guess I too have the I.Q. of a small rock. I like the analogy by the way

Hmm...I think my IQ must be that of a tiny piece of gravel...or maybe a grain of sand?

I started to think I don't have an IQ. Waaaaa, mama help me out of this one....

i'm beginning to think my iq is disappearing too after lack of education. grins

Monty Hall problem bugged me out years ago but I understood the idea at last and a relief got over my whole soul since then

If you attend such a contest switch the door..It's been a while since the question was posted, but I just happened upon it - so, here's my explanation as to why it IS better to switch.

The key is to remember that there are two cases. Either (1) you are going to stick with your door, or (2) you are going to switch.

Case 1:

You are going to stick with your door. Your original probability of choosing the correct door is 1 out of 3. Just because one of the goats is revealed, doesn't change that probability. So, if you are going to stick with your first choice, your probability of winning remains 1/3.

Case 2:

You are going to switch. Well, you have a 2 out of 3 chance of picking the wrong door from the start. If you did pick the wrong door, and then switch - you will be a winner. So, you have a 2/3 chance of picking wrong to begin with, and then switching to the winner.

Therefore, switching actually doubles your chances of winning.

I hope that helps!

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