17 min bridge crossing puzzle

Puzzle:
There are four people who want to cross a bridge; they all begin on the same side. You have 17 minutes to get them all across to the other side. It is night, and they have one flashlight. A maximum of two people can cross the bridge at one time. Any party that crosses, either one or two people, must have the flashlight with them.
The flashlight must be walked back and forth; it cannot be thrown, for example. Person 1 takes 1 minute to cross the bridge, person 2 takes 2 minutes, person 3 takes 5 minutes, and person 4 takes 10 minutes. A pair must walk together at the rate of the slower person’s pace. For example, if person 1 and person 4 walk across first, 10 minutes have elapsed when they get to the other side of the bridge. If person 4 returns the flashlight, a total of 20 minutes have passed and you have failed the mission.

9 card puzzle

Question:
9 cards are there. u have to arrange them in a 3*3 matrix.
cards are of 4 colors.they are red,yellow,blue,green.
conditions for arrangement: one red card must be in first row
or second row.2 green cards should be in 3rd column.Yellow
cards must be in the 3 corners only. Two blue cards must be in
the 2nd row. Atleast one green card in each row.

Daughters’ Ages

Question:
Two MIT math grads bump into each other at Fairway on the upper west side. They haven’t seen each other in over 20 years.

THE FIRST GRAD SAYS TO THE SECOND: “how have you been?”
SECOND: “great! i got married and i have three daughters now”
FIRST: “really? how old are they?”
SECOND: “well, the product of their ages is 72, and the sum of their ages is the same as the number on that building over there..”

FIRST: “right, ok.. oh wait.. hmm, i still don’t know”
SECOND: “oh sorry, the oldest one just started to play the piano”
FIRST: “wonderful! my oldest is the same age!”

problem: how old are the daughters?

100 Doors in a Row...microsoft puzzle

Question:

you have 100 doors in a row that are all initially closed. you make 100 passes by the doors starting with the first door every time. the first time through you visit every door and toggle the door (if the door is closed, you open it, if its open, you close it). the second time you only visit every 2nd door (door #2, #4, #6). the third time, every 3rd door (door #3, #6, #9), etc, until you only visit the 100th door.

question: what state are the doors in after the last pass? which are open which are closed?

Solution:

For example, after the first pass every door is open. on the second pass you only visit the even doors (2,4,6,8…) so now the even doors are closed and the odd ones are opened. the third time through you will close door 3 (opened from the first pass), open door 6 (closed from the second pass), etc..

Twin brother puzzle

Puzzle

You are travelling down a road to a village. You reach a fork in the road and find a pair of identical twin brothers standing there. One of the brothers always tells the truth and the other always lies.
If you are allowed to ask only one question to one of the brothers to find which is the correct road to the village, what is your question ?



Solution
Point to one of the roads in the fork and ask the following question to one of the brothers.
"If I ask your brother if this is the correct road to the village will he say yes or no?"
If he answers is "no" then it is the correct way to the village.
Think about it -

3 switches puzzle

Puzzle:

You have just walked into a dark two-storey house. There are three light switches on the first floor A, B and C. Only one of the switches works, and it turns on the light on the second floor.

You cannot see the second floor light from the first floor and there are no windows in the building, but you do have a flashlight.

You can only make one trip up the stairs, and you can only flip one switch at a time. How do you determine which of the three switches turns on the light on the second floor ?

Bridge Crossing in minimum time

Problem Statement:

Four people need to cross a rickety rope bridge to get back to their camp at night. Unfortunately, they only have one flashlight and it only has enough light left for seventeen minutes. The bridge is too dangerous to cross without a flashlight, and it’s only strong enough to support two people at any given time.

Each of the campers walks at a different speed. One can cross the bridge in 1 minute, another in 2 minutes, the third in 5 minutes, and the slow poke takes 10 minutes to cross. How do the campers make it across in 17 minutes?

Solution:

To get everyone across in 17 minutes, we need get the two slowest people across together; otherwise we are wasting too much time. Once we get them across, how do we not make one of them walk back with the flashlight?

arithmetic operators puzzle 3 1 3 6 =8

Puzzle:

Add arithmetic operators (plus, minus, times, divide) to make the following expression true: 3 1 3 6 = 8. You can use any parentheses you’d like.

Solution:

An interviewer is asking this problem to see how you think and approach problems—so

don’t just guess randomly.

Try approaching this the following way: What sorts of operations would get us to 8? 
I can think of a few:

4 * 2 = 8

16 / 2 = 8

4 + 4 = 8