probability question help

how would i do these two questions?

1. What is the probability of rolling AT LEAST one six in 7 rolls of a FAIR die.

2. you sample five fish from an lake where one in four fish carry a parasite, what is the probability that you will sample at least one parasitized fish? Assume that the population is so large that you are effectively sampling with replacement.

Thanks

Reply 1

TenOfThem

18

Original post by candyloveee

how would i do these two questions?

1. What is the probability of rolling AT LEAST one six in 7 rolls of a FAIR die.

2. you sample five fish from an lake where one in four fish carry a parasite, what is the probability that you will sample at least one parasitized fish? Assume that the population is so large that you are effectively sampling with replacement.

Thanks

What have you tried

Reply 2

candyloveee

OP

Original post by TenOfThem

What have you tried

i thought itd just be 1/6 * 7 for the first one..but that seems too easy to be right

Reply 3

candyloveee

OP

Original post by TenOfThem

What have you tried

and for the fish one, 1/4 * 5 . but again..i dont have the answers, so dont know whats right or wrong

Reply 4

TenOfThem

18

Original post by candyloveee

i thought itd just be 1/6 * 7 for the first one..but that seems too easy to be right

given 7/6>1 that cannot possibly be correct can it?

Work out the probability that NONE of the dice has a 6

Reply 5

TenOfThem

18

Original post by candyloveee

and for the fish one, 1/4 * 5 . but again..i dont have the answers, so dont know whats right or wrong

And, again, since 5/4>1 that is not possible

Reply 6

candyloveee

OP

i really dont know thats why im asking on here...

Reply 7

Giggles Shocker

don't you have to do some tree diagram to work it out first?

Reply 8

trouducul

prob to obtain a 6: 1/6
prob not to obtain a 6: 1- 1/6 = 5/6
prob not to obtain a 6 in 7 rolls :frown:

5/6)^7
prob to obtain at least a 6 in 7 rolls: 1- (5/6)^7

Reply 9

candyloveee

OP

so for i got

1. 0.721

2. 0.763

are these answers the same as what you guys got?

Reply 10

Giggles Shocker

i gave up... my brain dont work... wait a moment let me try again.....

Reply 11

Giggles Shocker

sorry cant do it.... i think im over complicating it for myself

Reply 12

trouducul

?

Original post by Giggles Shocker

sorry cant do it.... i think im over complicating it for myself

It's exactly the same procedure as in the first one.

prob that a fish has a parasite: 1/4
prob that a fish does not have a ***** parasite: 1- (1/4) = 3/4
prob that the 5 fish do not have parasite: (3/4)^5
prob that at least one of them has: 1-(3/4)^5

(edited 11 years ago)

probability question help

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