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Guilherme

Comments 3

3 Coins

SPOILER DON'T READ THIS BEFORE TRYING TO SOLVE THE PUZZLE SPOILER ************** * * * * * * * * * *

My answer:

First case. Since you are going to get heads twice it necessarily means you did not choose the Tails coin. This gives you two scenarios:

1 - 1/2 chance of choosing the fair coin times 1/2 chance of getting heads again. 2 - 1/2 chance of choosing the Heads coin times 1 chance of getting heads again,

(1/2 * 1/2) + (1/2 * 1) = 3/4 or 75%

For the second case. Three scenarios:

1 - 1/3 chance of choosing the Heads coin times 1 chance of getting Heads twice. 2 - 1/3 chance of choosing the Tails coin times 1 chance of getting Tails twice. 3 - 1/3 chance of choosing the fair coin, but since you've already got the same result twice, you only have the probability of getting the same outcome twice again which would be 1/2 * 1/2 = 1/4.

1/3 * (1 + 1 + 1/4) = 3/4 or 75%

Did this pretty quick, not sure if I'm right.

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Nice to meet you

**** SPOILER ALERT

Combination of N people in pairs:

N! / (2! * (N-2)!) = 45

N * (N - 1) = 90

N = 0 or N = 10 which is the answer.

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Cocktail Party

Simple combination: 7! / ( 2! * (7-2)! )

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Submitted Puzzles 1

9 6 The double-square number problem
It's said that a number N with 4 digits is a double-square number when it equals the sum of the squares of two numbers: one formed by the first two digits of N, in the order they appear in N and the ot ...
Hard
8.2