Friday, January 26, 2018

A Car on a Fragile Bridge

A car is crossing a 20km long bridge. The bridge can support at most 1500kg of weight over it. If somehow, the weight on the bridge becomes more than that, it will break.
Now, the weight of the car is exactly 1500kg. At the midway, a bird comes and sits on the roof of the car. This bird weighs exactly 200 gram. 

A Car on a Fragile Bridge
Can you tell if the bridge breaks at this point or not? 

Read what will happen next? 



Bridge Under Load

What was the situation?

At first look, the first impression would be that the bridge will break certainly. But if you wait for a while before concluding anything you will get the right answer.

The bridge will not break in the case! It's 20 km long bridge & now it's in the middle of bridge after traveling 10 km. By now, it must have used half of the fuel that was in the tank initially at the start. This amount of fuel must be weighing more than 200 gm. Hence even a bird sits on the car there are hardly any chances the total weight on the bridge goes beyond 1500 kg! Hence, no chance of breaking of it.

No way that bridge will break!

Saturday, January 13, 2018

Mixture of Coffee and Tea

Suppose we lay down two cups in front of you. One of the cups is filled with tea and the other one with coffee. Now we ask you to take a spoonful of tea and mix it with the coffee. 

At this moment, the coffee cup has a mixture of tea and coffee. You have to take that mixture (spoonful) and add it back to the tea. 

Can you now tell if the cup of coffee has more tea or the cup of tea has more coffee ?

Skip to the answer! 


Component Levels in Mixture

How mixture made?

After adding 1 spoon of tea into coffee, the levels of liquids in both cups must be unequal. Whatever now tea cup is missing is now in cup of coffee & mixed with coffee. The content of tea in the cup of coffee is certainly more.

Now after taking spoonful of the mixture back to tea cup the levels of the liquid in both cups would be same. Hence, whatever the cup of tea is missing is replaced by coffee. That missing tea content is now in the cup of coffee where it has replaced some of coffee content! 

Suppose there are 1000 molecules in each cup i.e. of tea & coffee. Let's assume 100 molecules of tea are mixed to coffee using spoon. Now, coffee cup will have 1100 molecules and tea will have 900 molecules. Obviously, right now the cup of coffee contains more tea (100 molecules) that coffee in cup of tea (0 molecules)!

Now while taking 100 molecules back from mixture having 1100 molecules, suppose 70 molecules of coffee & 30 of tea are taken. That means, exactly 100 - 30 = 70 molecules of tea left in mixture. That 70 + 30 molecules mixture is poured into cup of tea. That is exact 70 molecules of coffee mixed in tea.

What does it mean? 70 molecules of coffee have displaced 70 molecules of tea into cup of coffee maintaining level of both the liquids. 

We can say other way as well. 30 molecules of tea displaced 30 molecules of coffee into cup of tea while maintaining levels of both the liquids same. 

So the answer is both have same level of contents mixed.

Knowing Component Levels in Mixture

Monday, January 8, 2018

An Insepection by The Superintendent

One day, a class teacher was told that the school superintendent will be visiting her class on the next day. The superintendent can ask questions from anywhere and it can be easy as well as difficult. The teacher will have the liberty to choose any pupil for answering the question.

How to impress the Superintendent?

Now she is determined that the impression that is cast upon the superintendent after the inspection should be great. How will she instruct the students so that she maximizes the chances of receiving a correct answer for each question? Also, she must create the best impression. How will she do it? 

This is what she should do! 

To Impress Superintendent

What was the resolution of teacher? 

Now what should teacher do here is to devise the 'sign' language to communicate with students. Also she needs to make sure that the superintendent won't have any doubt while questioning students.

She should ask all the students to raise hands for every question that is being asked by superintendent. However, those who know correct answers should raise right hand & rest of all should raise left hand. This way she would be able to know the students who knows the correct answer & choose any of them to answer the question.

All raised hands to each question would definitely leave great impression on the superintendent.

Sign language to communicate while inspection

Note : We are assuming superintendent not smart enough to notice that students raising different hands for different questions.

Saturday, January 6, 2018

Generous Devotee

A devotee visits 9 temples when he visits India. All these nine temples have one thing in common - there are 100 steps in every temple. The devotee puts Re.1 coin after climbing up every step. He does the same while climbing down every step. At each temple, the devotee offers half of his money from his pocket to god. In this way, his pocket becomes empty after his visit to 9th temple.

How much donated by the devotee?

Can you calculate the total amount he had initially ? 

Click here to know exact amount! 

Donations By The Devotee

Why to calculate those?

Using algebraic equations in the case can make things complicated unnecessarily. Hence, we would start from backward. Before putting 100 coins on steps while climbing down 9th temple devotee must had 100 coins. That means he had 200 coins when he climbed up the 9th temple half of which i.e. 100 he offered to that temple & 100 put on the 100 steps of 9th temple. Moreover, he must have placed 100 coins while climbing up 9th temple. So before visit to 9th temple he must had, (100 x 2) + 100 = 300 coins.

Same way, finding the amount he had before visit to each temple like below.

Before eight temple: (300+100)*2 + 100 = 900
Before seventh temple: (900+100)*2 + 100 = 2100
Before Sixth temple: (2100+100)*2 + 100 = 4300
Before fifth temple: (4300+100)*2 + 100 = 8900
Before fourth temple: (8900+100)*2 + 100 = 18100
Before third temple: (18100+100)*2 + 100 = 36,500
Before second temple: (36500+100)*2 + 100 = 73300
Before first temple: (73300+100)*2 + 100 = 146900

Calculation of Donations By The Devotee
To conclude,  he had Rs. 146900 initially.  


Tuesday, January 2, 2018

Cars Across the Desert

A military car carrying an important letter must cross a desert. 

There is no petrol station on the desert and the car has space only for petrol that lasts to the middle of the desert.

There are also other cars that can transfer their petrol into one another.

How can the letter be delivered?

Delevering letter across the desert

This is how letter can be delivered!


Delivering Letter Across The Desert

What was the task?

We need 4 such cars to deliver the letter across the desert successfully.

Let's divide the entire route into 6 parts. That means the distance that car can travel (half the total path in desert) is divided into 3 parts. To travel each part car requires 1/3rd of it's petrol in the tank.

1. At first 1/6th of total path, all cars are 2/3rd full. Now 2/3rd of the petrol from 1 car can be used to fill 1/3rd of tanks in other 2 cars (1/3 + 1/3 = 2/3). This way, we would have 2 cars full while 1 car 2/3rd full. We are leaving behind the empty car, taking 3 cars forward.

Journey of Letter Across The Desert
Stage 1

2. At next 1/6th of the distance, 2 full cars will use 1/3rd of their petrol hence would be 2/3rd full. And the car that was 2/3rd at previous stage would be not 1/3rd full. At this stage, the petrol from car that is 1/3rd full can be used to fill tank of 1 car completely. So we are leaving behind one another empty car here & taking fully filled car & 2/3rd filled car for next stage.

Journey of Letter Across The Desert
Stage 2

3. For next 1/6th of the total distance, the car that was fully filled would have 2/3rd petrol. And the car which was 2/3rd at previous stage would be now 1/3rd filled. The petrol of this car can be used to fill the tank of the first car. Now we have 1 car fully filled while other one is empty. So we can leave behind the empty car & use fully filled car for the rest half of the journey. Remember, a car which tank is full can travel half the total path.

Journey of Letter Across The Desert
Stage 3

Monday, January 1, 2018

Who Works Where?

Alex, Betty, Carol, Dan, Earl, Fay, George and Harry are eight employees of an organization
They work in three departments: Personnel, Administration and Marketing with not more than three of them in any department.

Each of them has a different choice of sports from Football, Cricket, Volleyball, Badminton, Lawn Tennis, Basketball, Hockey and Table Tennis not necessarily in the same order.

1.Dan works in Administration and does not like either Football or Cricket.

2.Fay works in Personnel with only Alex who likes Table Tennis.

3.Earl and Harry do not work in the same department as Dan.

4.Carol likes Hockey and does not work in Marketing.

5.George does not work in Administration and does not like either Cricket or Badminton.

6.One of those who work in Administration likes Football.

7.The one who likes Volleyball works in Personnel.

8.None of those who work in Administration likes either Badminton or Lawn Tennis.

9.Harry does not like Cricket.

Find the department & Favorite sport of each employee.
Who are the employees who work in the Administration Department?

In which Department does Earl work?

Who is the fan of each sports?

Click here for the complete picture. 


Employees of Each Department

What was the data given? 

Let's make a table where columns represent the sport & row represents the employee.There are 3 tables 1 for each department. To make table shorter we will use the initials only of sports' & employees' names as below.

Possible Deparment & Favorite Sport of Each Employee

A - Alex, B - Betty, C - Carol, D - Dan, E - Earl, F - Fay, G - George, H - Harry. 

F - Football, C - Cricket, V - Volleyball, Bd - Badminton, LT - Lawn Tennis, Bs - Basketball,
H - Hockey, TT - Table Tennis  

Now taking clues one by one into consideration.

1. Dan works in Administration and does not like either Football or Cricket.

Possible Deparment & Favorite Sport of Each Employee
Table 1

2. Fay works in Personnel with only Alex who likes Table Tennis.

This indicates that Alex is working in Personnel department & likes Table Tennis. Fay working in same department may like any other sports than Table Tennis. No body other working in this department.

Possible Deparment & Favorite Sport of Each Employee
Table 2
3. Earl and Harry do not work in the same department as Dan.

Hence they must be working in Marketing department!

Possible Deparment & Favorite Sport of Each Employee
Table 3
4. Carol likes Hockey and does not work in Marketing.

That's why his department must be Administration.

Possible Deparment & Favorite Sport of Each Employee
Table 4
5. George does not work in Administration and does not like either Cricket or Badminton.

His department must be Marketing & he might be liking Football or Volleyball or Lawn Tennis or Basketball.

Possible Deparment & Favorite Sport of Each Employee
Table 5