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10 6 Sum of Two Prime Numbers
If p, q > 2 are consecutive in set of primes. Since p,q can only be odd number, (p+q) is an even number. Can (p+q)/2 be prime? from http://republicofmath.com/
Submitted by MoralMachine
Easy
3.2
3 6 How many?
As I was going to St. Ives, I met a man with seven wives. Each wife had seven sacks. Each sack has seven cats. Each cat had seven kits. Kits, cats, sacks, and wives, How many were going to St. Ives? ...
Submitted by Gene
Easy
2.8
9 9 1978
The year 1978 is such that the sum of the first two digits and the latter two digits is equal to the middle two digits, i.e. 19 + 78 = 97. What is the next year (after 1978) for which this is true?
Doable
6.6
9 9 The Monty Hall Problem
You’re on a game show, and you’re given the choice of three doors: Behind one door is a car and behind the other two doors are goats. You pick a door, say No. 1, and the host, who knows what’s behind ...
Doable
5.5
8 3 The Tallest Mountain
A man approaches you with a very enigmatic look on his face. He asks your for a bit of your time and if you could answer a quick question for him. He asks: “Before Mt. Everest was discovered, which w ...
riddle Submitted by Ravi
Easy
2.3
4 3 The Middle of Nowhere
What is in the middle of "nowhere"? The answer is indisputable, and not based on some philosophy.
riddle Submitted by Aakash
Easy
2.4
8 5 Prisoners and hats
100 prisoners are standing in a line each 1 seeing the back of the ones in front of him. Each prisoner is given a black or a white hat. If they can guess the color of their hat they can go away freel ...
logic brain teaser Submitted by Valentin
Hard
8.5
10 3 Measuring Up
You have a 3 and a 5 litre water container, each container has no markings except for that which gives you its total volume. You also have a running tap. You must use the containers and the tap in su ...
logic brain teaser Submitted by Ravi
Easy
3.1
10 2 Two Trains
Two trains (Train A and B) with 200 km between them are travelling towards each other at 100km/h. A mosquito, initially standing on the front of Train A, starts travelling towards Train B at 150km/h. O ...
Math physics rates Submitted by Ravi
Doable
4.5
12 1 Choose the Next Letter
Choose the next letter in the sequence: O T T F F S S ?
logic patterns sequences Submitted by Ravi
Doable
4.0
7 2 Burning Rope
There are two lengths of rope. Each one can burn in exactly one hour. They are not necessarily of the same length or width as each other. They also are not of uniform width (may be wider in middle th ...
Submitted by Ravi
Doable
4.3
8 8 Interview Question - Databases
This is a common interview question at companies like Google and Amazon: “Explain a database in three sentences to your eight-year-old nephew.” This question has an infinite number of solutions. Fee ...
Easy
2.7
5 6 Cooking Time
A cook must put a souffle exactly 9 minutes at the oven, but he only have a 7 minutes hourglass and a 4 minutes hourglass. How can he measure 9 minutes with those clocks?
logic Submitted by Ravi
Doable
5.6
6 5 Clock Works - Google Interview Question
How many degrees are there in the angle between the hour and minute hands of a clock when the time is a quarter past three?
Easy
3.1
8 8 The Famous Hole in a Sphere
This incredible problem was first made famous by Martin Gardner with his ‘Mathematical Games’ column published in Scientific American throughout the 60s and 70s. A cylindrical hole, 6 inches long, ...
Math Lateral geometry Submitted by Ravi
Hard
6.7