1.A multiple choice test contains four choices (a,b,c,d) for each question.You guess randomly on two questions on the test.

Heres what i gotta do:
A.Make a tree diagram of the possible answers for the two questions.

B.What is the probability that you answer both questions correctly?

C.Suppose the answer to both questions is A.Use the tree diagram to count how many outcomes there are in which you answer at least one of the two questions correctly.What is the probability that you answer at least one question correctly?

Second problem

2.You remember part of your friends 7 digit phone number but you cannot remember the rest.

a.Your friends number begins with 79 and ends with five other digits.How many different phone numbers can begin with 79?

b.You remember that the next digit after 79 is 8.How many possible phone numbers can begin with 798?

c.How many digits of a 7 digit phone number do you have to know before the probability that you can randomly guess the number correctly on the first try is 1/100 <-- supposed to be a fraction.

I really need help,How the heck do i do this?????

Post edited at 10:14 am on Sep. 7, 2008 by Vincent Valentine14

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The heart of a Champion,The concience of a Hero.
Screw you,I hope you burn in hell you b*tch.

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uhm..do you have msn?

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yeah

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The heart of a Champion,The concience of a Hero.
Screw you,I hope you burn in hell you b*tch.

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why dont you just attempt them and we can point out what you did wrong

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good idea

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Find something worth dying for and live for it.

Heres what i gotta do:
A.Make a tree diagram of the possible answers for the two questions.

Learn how to draw a tree diagram through some internet or something.. it's easy but i don't want to pull up paint to do it.

B.What is the probability that you answer both questions correctly?
P(q1 = A, q2=A) = P(q1 =A)*P(q2=A) = 1/4*1/4 = 1/6

C.Suppose the answer to both questions is A.Use the tree diagram to count how many outcomes there are in which you answer at least one of the two questions correctly.What is the probability that you answer at least one question correctly?

Let's just take the conjugate:
1- P(p1 != A, p2 !=A) = 1 - (3/4)(3/4) = 7/16

Second problem

2.You remember part of your friends 7 digit phone number but you cannot remember the rest.

a.Your friends number begins with 79 and ends with five other digits.How many different phone numbers can begin with 79?
you got 5 spaces, and each of them can be 0-9
so it's going to be:
10^5

b.You remember that the next digit after 79 is 8.How many possible phone numbers can begin with 798?
10^4... same idea

c.How many digits of a 7 digit phone number do you have to know before the probability that you can randomly guess the number correctly on the first try is 1/100 <-- supposed to be a fraction.

5.. duh! you need 10^2 possible choices..

those problems are intuitive and should never be missed.