statistics
posted by Christine .
you have 8 blue marbles, 7 red marbles, and 5 green marbles. What is the probability of obtaining at least 2 red marbles in three draws with replacements?
I have the answer, just can't figure out how to get it.
Thanks!

Seven out of the twenty are red. The probability of NOT getting ANY red in three tries is (13/20)^3 = 0.2746
The probability of getting only one red is 3*(13/20)^2*(7/20) = 0.4436
The probability of getting two or more is 1  0.2736  0.4436 = 0.2828 
I thought I was understanding this but I am really not sure about the symbols.
Does the 3*(13/20)^2*(7/20) translate to 3 times 13/20 times 2 times 7/20?
Sorry I am not up on the symbols...
I will keep trying. 
3*(13/20)^2*(7/20)
means
three times (13/20) squared times (7/20)
in general the probability of getting r successes out of n tries in binomial distribution if probability of success is p is
P(r) = C(n,r) p(r)^r (1p)^(nr) 
That is even more confusing. I am totally lost on this problem.
I know that I have to multiply the three possibilities, so (7/20)(7/20)(13/20) three times (same numbers, different order) and I get 0.07963. I thought I would add those three numbers or essentially multiply that number by three, however, I did not get the right answer doing it that way.
Thanks for any help. I am totally confused.
Respond to this Question
Similar Questions

math
George has a bag of marbles. Inside the bag are 5 red marbles, 3 green marbles, and 2 blue marbles. He draws out two marbles in a row, without replacement. What is the number of outcomes? 
Algebra
Out of jar with 100 marbles, 49 are blue marbles, 7 are green marbles, 27 are red marbles and 17 are yellow marbles. What is the probability of drawing a red marble? 
probability
George has a bag of marbles. Inside the bag are 5 red marbles, 3 red marbles, and 2 blue marbles. He draws out two marbles in a row, without replacement. What is the number of outcomes? 
math
sally has a bag with red,blue, and green marbles. She has twice as many blue marbles as red marbles. She has 5 times as many green marbles as red marbles. Altogether she has 24 marbles. How many of each color marble does she have? 
Discrete Math
A bag contains 5 red marbles, 4 yellow marbles, 3 green marbles, 2 orange marbles and 2 purple marbles. If three marbles are removed, what is the probability that at least one of them is red? 
math
A bag contains 5 red marbles, 6 white marbles, and 8 blue marbles. You draw 5 marbles out at random, without replacement. What is the probability that all the marbles are red? 
Math
A bag contains 9 red marbles, 8 white marbles, and 6 blue marbles. You draw 4 marbles out at random, without replacement. What is the probability that all the marbles are red? 
Math
I am having a problem answering this math problem. Andrea has a box of marbles in it. She has seven red marbles, thirteen blue marbles and nineteen yellow marbles. If she reaches in and takes out marbles without looking, what is the … 
Math "Need Help Asap"!
1.)There are 35 marbles in a bag:9 blue marbles, 8 marbles, 4 red marbles, 4 red marbles, 8 white marbles, & 6 yellow marbles. Find P(Red). Write the probability as a fraction in simplest form, a decimal, & a percent. A.)4/31, 0.129, … 
Math
A bowl has red,green and blue marbles.There are 95 red marbles.the nuber of blue marbles is 5 timesthe number of green mables altogether red and green marbles are 189 less then blue marbles .how may marbles are there in total