Logical Reasoning Puzzles With Answers | Best Riddles and Brain Teasers

#1 - River Riddle

Four people need to cross a dark river at night.They have only one torch and the river is too risky to cross without the tourch. if all people cross simultanoesly then torch light wont be sufficient.Speed of each person of crossing the river is different.cross time for each person is 1 min, 2 mins, 7 mins and 10 mins. What is the shortest time needed for all four of them to cross the river ?

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The initial solution most people will think of is to use the fastest person as an usher to guide everyone across. How long would that take? 10 + 1 + 7 + 1 + 2 = 21 mins. Is that it? No. That would make this question too simple even as a warm up question.

Let's brainstorm a little further. To reduce the amount of time, we should find a way for 10 and 7 to go together. If they cross together, then we need one of them to come back to get the others. That would not be ideal. How do we get around that? Maybe we can have 1 waiting on the other side to bring the torch back. Ahaa, we are getting closer. The fastest way to get 1 across and be back is to use 2 to usher 1 across. So let's put all this together.

1 and 2 go cross
2 comes back
7 and 10 go across
1 comes back
1 and 2 go across (done)

Total time = 2 + 2 + 10 + 1 + 2 = 17 mins

#2 - Logical Thinking Riddle

I have 100 coins in my wallet.

What is the minimum number of coin(s), i would be required in order to make sure each coin touched exactly three other coins.

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4

3 placed flat on the table in a triangle(touching each other) and put the fourth one on top of them in the middle.

#3 - Maths Logic Riddle

It can be easily calculated that the digits 0 to 9 can be arranged into 3628800 distinct ten-digit numbers.

But I also know how many of these numbers are prime.

Do you?

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Zero

The sum of numbers from zero to nine is 45 and can be divisible by 3 and 9.

#4 - Trolls Riddle

You are on your way to visit your Grandma, who lives at the end of the valley. It's her birthday, and you want to give her the cakes you've made.

Between your house and her house, you have to cross 7 bridges, and as it goes in the land of make believe, there is a troll under every bridge! Each troll, quite rightly, insists that you pay a troll toll. Before you can cross their bridge, you have to give them half of the cakes you are carrying, but as they are kind trolls, they each give you back a single cake.

How many cakes do you have to leave home with to make sure that you arrive at Grandma's with exactly 2 cakes?

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2: At each bridge you are required to give half of your cakes, and you receive one back. Which leaves you with 2 cakes after every bridge.

#5 - Logic Math Problem

In Sahara desert , 3 men found a big 24L Jar is full of water. Since there is shortage of water so they decided to distribute the water among themselves such that they all have equal amounts of it. But they only have a 13L, a 5L and an 11 liter Jar.

How do they do it?

$Logic Math Problem$

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24 13 11 5
----------
24 0 0 0
11 13 0 0
6 13 0 5
6 2 11 5
8 0 11 5
8 5 11 0
8 13 3 0
8 8 3 5
8 8 8 0

#6 - Distance Problem

Two towns are exactly 100 km apart. Rakesh leaves City A driving at 30 km/hr and Harish leaves City B a half an hour later driving 60 km/hr. Who will be closer to City A when they meet?

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Both would be the same distance from City A.

#7 - chacha chaudhary Puzzle

chacha chaudhary(name of a person) is convicted in Germany. He gets the death penalty. The judge allows him to say a last sentence in order to determine the way the penalty will be carried out. If he lies, he will be hanged, if he speaks the truth he will be beheaded. The perspn speaks a last sentence and to everybody surprise some minutes later he is set free because the judge cannot determine his penalty.What did chacha chaudhary said?

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chacha chaudhary said: 'I shall be hanged!' If he was lying, he would be hanged. But that's what the chacha was saying. So he speaks the truth. But if he speaks the truth, he would be beheaded, so then he was not speaking the truth. So it is impossible for the judge to determine wether the person speaks the truth or not. So therefore the judge cannot determine the penalty and sets him free.

#8 - Sachin Red Ferrari Number Riddle

Sachin Tendulkar bough a red ferrari with a strange 5 digit numbered plate.The water image of the number is 78633 more than my car number.All the digits of sachin's car number are distinct.

What is the original number on sachin's number plate?

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10968
Water image is 89601

#9 - Simple Logical Problem

Michael have ten pairs of black socks, eight pairs of white socks and seven pairs of green socks. Everything is mixed in a draw. As there is no light he were not able to identify the color of the socks. How many of the socks did he want to take to match one pair

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Although there are many socks in the draw, there are only three colors. So, four socks are enough to match one pair.

#10 - Hourglass Time Puzzle

There are 2 sand hourglasses.
The small one can measure 5 hours and the large one can measure 7 hours.

How can we measure 16 hours with 2 sand hourglasses running together ?

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Steps:
* Start both sand hourglasses at the same time.
* You flip over the small sand hourglass when it finishes the first 5 hours.
* Flip over the large one when it finishes its first 7 hours.
* When the small sand hourglass runs to 10 hours, flip over the small and large sand hourglass at the same time. It means the large sand hourglass will run 3 hours again. When the large sand hourglass run to 13 hours (7 + 3 + 3), flip both the small and large sand hourglass over again to run another 3 hours.