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- Jan 31st 2007, 03:47 PM #1

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## Me and Probabilitys are having a problem

Ive got a few questions if someone could help out. Thanks so much. I love this site.

1. In one town of 54% democrates of 2 randoml y selected for a survey. Find the probability that they are both democrates??

2. Find the probability of correctly answering the 1st 2 questions on a multiple choice test if random questions are made and each question have 5 possible answers?

3. You are dealt 2 cards from a shuffled deck of 52 playing cards. find the probability that both cards will be black.

If you could show the break down so i can get the consept.. Thank you. I wish i could help someone. Not in this subject.

- Jan 31st 2007, 10:32 PM #2

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- Jan 31st 2007, 10:36 PM #3

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The probability of getting the right answer to a question by choosing answers

randomly is 1/5=0.2 (or 20%), as there ia one correct answer out of a total

of five possibilities.

Now the answer proceeds as for question 1.

Probability of getting first question right is 0.2, and of getting the second

right is also 0.2. So the probability of getting both right is 0.2*0.2=0.04

(or 4%).

Note that this works because the result of the first choice does not effect

the second choice. We will see in the next question a situation where this

is not true.

RonL

- Jan 31st 2007, 10:40 PM #4

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The probability that the first card selected is black is 26/52, as there are

26 black cards amoung a total of 52 cards.

Now the probability that the second card is black given that the first was

black is 25/51, as there are 25 black cards remaining out of a total or 51 cards remaining.

So the probability that both cards are black is:

(26/52)*(25/51) ~= .2451,

or about 24.5%

RonL

- Feb 1st 2007, 03:36 PM #5

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- Feb 1st 2007, 09:20 PM #6

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