A man lives on the 44th floor of his building. On rainy days, when he gets home from work, he takes the elevator all the way up to his floor. But on sunny days, he goes up to floor 20 and walks the rest of the way. Why does he do this?
The man is a midget and cannot reach button "44" in the elevator on sunny days. On rainy days he has his umbrella with him and is able to use it to press the button.
See also best riddles or new riddles.logicmathshort
Is half of two plus two equal to two or three?
Three. It seems that it could almost be either, but if you follow the mathematical orders of operation, division is performed before addition. So... half of two is one. Then add two, and the answer is three.logic
You have just purchased a small company called Company X. Company X has N employees, and everyone is either an engineer or a manager. You know for sure that there are more engineers than managers at the company.
Everyone at Company X knows everyone else's position, and you are able to ask any employee about the position of any other employee. For example, you could approach employee A and ask "Is employee B an engineer or a manager?" You can only direct your question to one employee at a time, and can only ask about one other employee at a time. You're allowed to ask the same employee multiple questions if you want.
Your goal is to find at least one engineer to solve a huge problem that has just hit the company's factory. The problem is so urgent that you only have time to ask N-1 total questions.
The major problem with questioning the employees, however, is that while the engineers will always tell you the truth about other employees' roles, the managers may lie to you if they like. You can assume that the managers will do their best to confuse you.
How can you find at least one engineer by asking at most N-1 questions?
You can find at least one engineer using the following process:
Put all of the employees in a conference room. If there happen to be an even number of employees, pick one at random and send him home for the day so that we start with an odd number of employees. Note that there will still be more engineers than managers after we send this employee home.
Then call them out one at a time in any order. You will be forming them into a line as follows:
If there is nobody currently in the line, put the employee you just called out in the line.
Otherwise, if there is anybody in the line, then we do the following. Let's call the employee currently at the front of the line Employee_Front, and call the employee who we just called out of the conference room Employee_Next.
So ask Employee_Front if Employee_Next is a manager or an engineer.
If Employee_Front says "manager", then send both Employee_Front and Employee_Next home for the day.
However, if Employee_Front says "engineer", then put Employee_Next at the front of the line.
Keep doing this until you've called everyone out of the conference room. Notice that at this point, you'll have asked N-1 or less questions (you asked at most one question each time you called an employee out except for the first employee, when you didn't ask a question, so that's at most N-1 questions).
When you're done calling everyone out of the conference room, the person at the front of the line is an engineer. So you've found your engineer!
But the real question: how does this work?
We can prove this works by showing a few things.
First, let's show that if there are any engineers in the line, then they must be in front of any managers.
We'll show this with a proof by contradiction. Assume that there is a manager in front of an engineer somewhere in the line. Then it must have been the case that at some point, that engineer was Employee_Front and that manager was Employee_Next. But then Employee_Front would have said "manager" (since he is an engineer and always tells the truth), and we would have sent them both home. This contradicts their being in the line at all, and thus we know that there can never be a manager in front of an engineer in the line.
So now we know that after the process is done, if there are any engineers in the line, then they will be at the front of the line. That means that all we have to prove now is that there will be at least one engineer in the line at the end of the process, and we'll know that there will be an engineer at the front.
So let's show that there will be at least one engineer in the line. To see why, consider what happens when we ask Employee_Front about Employee_Next, and Employee_Front says "manager". We know for sure that in this case, Employee_Front and Employee_Next are not both engineers, because if this were the case, then Employee_Front would have definitely says "engineer". Put another way, at least one of Employee_Front and Employee_Next is a manager. So by sending them both home, we know we are sending home at least one manager, and thus, we are keeping the balance in the remaining employees that there are more engineers than managers.
Thus, once the process is over, there will be more engineers than managers in the line (this is also sufficient to show that there will be at least one person in the line once the process is over). And so, there must be at least one engineer in the line.
Put altogether, we proved that at the end of the process, there will be at least one engineer in the line and that any engineers in the line must be in front of any managers, and so we know that the person at the front of the line will be an engineer.logic
Six jugs are in a row. The first three are filled with coke, and the last three are empty. By moving only one glass, can you arrange them so that the full and the empty glasses alternate?
Move and then pour all coke from second glass to fifth glass.logicmathshort
Hockey Stick and ball cost $50. If the Stick cost $49 more than the ball. What is the cost of each ?
Hockey Stick $49.50 & ball $0.50.logicmystery
It was a man's birthday. He lay dead in the lounge room of his house. Next to his body was a note, written in pencil. The note read 'Happy Birthday, Friend'. The victim had a girlfriend and the police suspected her ex-boyfriend. They could find no obvious evidence. While searching the ex-boyfriend's car, the police saw an envelope with the girlfriend's address written on it. They thought they would get the handwriting checked against the note. The scientist in charge came in early to work the next day; it was 7am. He looked out his window which faced east and stared at the rising sun and it was then that he realised how to prove the ex-boyfriend killed the man, even though the girlfriend's address was not written in the same handwriting. How did he do it?
The scientist's office faced east, and the sun was coming in through the window at a very low angle. He saw some very faint shadows on the surface of the envelope. He looked closer. There were the words embossed on the paper. They read "Happy Birthday, Friend". The ex-boyfriend had forgotten that a pencil leaves an impression on paper beneath the page written on.cleanlogicmathshort
Would you have more money with a million dollars today or a penny today and double your money every day for 31 days?
Second option. Double your money every day for 31 days.cleanlogicshort
Can you spot what's wrong with the following sentence?
PETER WAS ANGRY AT
HIMSELF BECAUSE HE
ACCIDENTALLY LEFT THE
THE KEYS TO HIS CAR
AT HIS FRIEND'S HOUSE.
It contains the word "THE" twice in a row.logic
Bill and Stacie are delighted when their new baby, Patrick, is born on February 29th, 2008. They think it's good luck to for him to be born on the special day of the leap year. But then they start thinking about when to celebrate his next birthday. After some thought, they decide that they want to celebrate Patrick's next birthday (when he turns 1) exactly 365 days after he was born, just like most people do.
What will be the date of this birthday?
The date of the birthday will be February 28th, 2009.
At first it might seem like his birthday should be March 1st, 2009, since February 29th is the day after February 28th in the leap year, while March 1st is the day after February 28th in non-leap years. But this is the wrong way to think about it.
The right way to think about it is that 365 days after the day before March 1st is always February 28th, regardless of whether it's a leap year or not. So Patrick's birthday will be February 28th.cleanfunnylogicshort
What is represented by this BrainBat Pattern?
EST EST EST EST
In a new Engineering Hostels they have 100 rooms. Ankit Garg was hired to paint the numbers 1 to 100 on the doors. How many times will Ankit have to paint the number eight ?