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Need Probability/Statistics help

So, I don't understand probability at all! I am feeling so hopeless right now. If anyone can help me with how to solve a couple of questions, I'll be eternally thankful!
Any help will be greatly appreciated!

Here are the questions:
1. Consider the events A and B, where P(A)=2/5, P(B')=1/4 and P(A U B)=7/8.
(a) Write down P(B).
(b) Find P(A and B)
(c) Find P(A|B).

and

The heights of boys at a particular school follow a normal distribution with a standard deviation of 5 cm. The probability of a boy being shorter than 153 cm is 0.705.
(a) Calculate the mean height of the boys.
(b) Find the probability of a boy being taller than 156 cm.

April 10, 2012

5 Comments • Newest first

LordZubin

[quote=RussainBoy]The heck is P(B')?

Only did 1 week of probability/statistics last year, didn't learn much/can't remember much.[/quote]

P(B') = P(~B) = the probability of not B.

Reply April 10, 2012
cutie

@Baller305: Yes, thank you!

Regrettably, I still don't understand 2. But its okay, thank you so much! :}

Reply April 10, 2012 - edited
cutie

@RussainBoy: I didn't have the formula chart. I just found it. lol
@Baller305: Can you justify/explain your answers please?

Reply April 10, 2012 - edited
cutie

I've no idea... All I know is the formula is P(B)+P(B')=1.

Math is yucky! -___-

Reply April 10, 2012 - edited
cutie

@RussainBoy: P(B') is 1/4. So, I think P(B) should be 3/4?

And oh great...
After three hours+ of agony, I got:
1 a) 3/4
b) 3/10
c) 2/5...

Reply April 10, 2012 - edited