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# Cumulative Probability Distribution watch

1. I'm really stuck on this question.

An archer hits the bullseye with a probability 0.6. She shoots 20 arrows at a time.
a) Find the probability that she hits with at least 50% of her arrows. She shoots 12 sets of 20 arrows.
b) Find the probability that she hits with at least 50% of her arrows in 7 of the 12 sets of arrows.
c) Find the probability that she hits with at least 50% of her arrows in fewer than 6 sets of arrows

I've done similar questions before with my calculator but this is more complicated. The book says the answers (a- 0.8725 b- 0.01027 c-0.0002407) but i have no idea how to get there.

Any help is appreciated
I'm really stuck on this question.

An archer hits the bullseye with a probability 0.6. She shoots 20 arrows at a time.
a) Find the probability that she hits with at least 50% of her arrows. She shoots 12 sets of 20 arrows.
b) Find the probability that she hits with at least 50% of her arrows in 7 of the 12 sets of arrows.
c) Find the probability that she hits with at least 50% of her arrows in fewer than 6 sets of arrows

I've done similar questions before with my calculator but this is more complicated. The book says the answers (a- 0.8725 b- 0.01027 c-0.0002407) but i have no idea how to get there.

Any help is appreciated

So you can define the question using a binomial distribution: X ~ B(20, 0.6)
3. (Original post by Caecilius_)
So you can define the question using a binomial distribution: X ~ B(20, 0.6)
I've tried doing that but it doesn't give me the correct answer.
I tried a few ways. I tried that with 10 as X and then with 120 as X and 240 as N
I've tried doing that but it doesn't give me the correct answer.
I tried a few ways. I tried that with 10 as X and then with 120 as X and 240 as N
Using X ~ B(20, 0.6),

Doing P(X>= 10) gives 0.8725.

Remember that P(X>= 10) = 1 - P(X<=9)
5. (Original post by caecilius_)
using x ~ b(20, 0.6),

doing p(x>= 10) gives 0.8725.

Remember that p(x>= 10) = 1 - p(x<=9)
Thank you, it was so obvious and i couldn't see it
I'm really stuck on this question.

An archer hits the bullseye with a probability 0.6. She shoots 20 arrows at a time.
a) Find the probability that she hits with at least 50% of her arrows. She shoots 12 sets of 20 arrows.
b) Find the probability that she hits with at least 50% of her arrows in 7 of the 12 sets of arrows.
c) Find the probability that she hits with at least 50% of her arrows in fewer than 6 sets of arrows

I've done similar questions before with my calculator but this is more complicated. The book says the answers (a- 0.8725 b- 0.01027 c-0.0002407) but i have no idea how to get there.

Any help is appreciated
Also, the "She shoots 12 sets of 20 arrows." is for part (b) right?
Thank you, it was so obvious and i couldn'tt see it
no problem
8. (Original post by Caecilius_)
Also, the "She shoots 12 sets of 20 arrows." is for part (b) right?
I'm not sure cause I didn't get that far

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