[mashpotatobunny]

I feel so nerdy asking here but I didn't know where else to turn to. Anywho, I have this one problem that I don't know how to figure out. Not sure what the distribution is for this problem so I'm stuck. Please help me figure it out:


A 'sonar' system detects submarines with 90% accuracy. The system operates independently from one submarine to the next.

(a) Of the next 20 submarines, what is the probability the system will not detect exactly 2?

The answer is 0.2852.


I would be forever grateful if you could help. Thank you so much!

[I Cook With A Flashlight]

2. TOPICS NOT ALLOWED IN GENERAL DISCUSSION.

Homework threads (these go into Pre-College) This means surveys, research help, equations, etc for school!!!! Do not post them here, they will be moved!

Read the rules next time.

[mashpotatobunny]

Oh, I'm sorry, I didn't know. I'm actually in college, so I wasn't aware I needed to go to Pre-College... XD Again, I apologize. Moderators, can you remove the topic, please?

[alicimoo]

This is a binomial problem.

Therefore, you need to use the equation
Pn(k) = (n C k)(p^k)q^(n-k)

n = total # of trials
k = # of successes
p = probability of success
q = 1 - p

I'm currently without a graphing calculator, so I just set success as NOT detecting 2.
p = 0.1
q = 0.9
k = 2
n = 18

n C k = n!/[k!(n-k)!]
20 C 2 = 20!/[2!(20-2)!]
20 C 2 = 20!/[2!18!]
20 C 2 = 380/2
20 C 2 = 190

So the answer is
190(0.1^2)(0.9^18) = 0.285178..etc.

------------------------------------------
If you define success as the system detecting the submarine, then it would be
p = 0.9
q = 0.1
k = 18
n = 20

(20 C 18)(0.9 ^18)(0.1 ^2) which should also be 0.285178...etc.

-------------------------------------------
What I showed you was the long way of solving it without a graphing calculator. There should be a program in your calculator that solves this type of problem. It's called binompdf(

This site will show you how to get there.
http://www.wonderhowto.com/how-to/video/ho...or-244044/view/

[Xcellerator]

Go, alicimoo !
Good thing I passed Stats this year with a 3 and my college takes it for credit. I totally forgot everything now. xD

[eternal_bliss]

Hope you did well on the test.