Quick Question (1 Viewer)

[KungPow]

A box has 4 geography books and 3 maths books in it. Two books are selected from random from the box.

If I wanted to find the probability of say, getting 2 geography books, would that be with replacement or without in terms of the wording of the question?

EDIT

Oh and another one. Slightly longer:
A number of electrical components are wired to an alarm so that it will operate if at least one of the components works. The probability that each of these components will work is 0.6

Find the minumum number of components needed to be 99% certain the alarm will operate.

Is the answer 6?

 

[ay_caramba]

i would think without replacement...they should specify that in the question tho

 

[SpaceMonkey]

Bad question.. doesn't really say.

 

[bloodysunday]

they really should say in the question whether you're replacing it or not, but i think my teacher told me a while back that with questions like that you should default to no replacement. or you could make sure and do it both ways

 

[jumb]

Oh and another one. Slightly longer:
A number of electrical components are wired to an alarm so that it will operate if at least one of the components works. The probability that each of these components will work is 0.6

Find the minumum number of components needed to be 99% certain the alarm will operate.

Is the answer 6?

Are the components in series or parallel?

 

[velox]

the first one should be without replacement, as he is taking the books at once. * i think *

 

[KungPow]

Are the components in series or parallel?

Well the question said "it will operate if at least one component works" so I'll assume parallel.

 

[KungPow]

the first one should be without replacement, as he is taking the books at once. * i think *

But shouldn't there only be 'without replacement' if you take the books one after another? Taking them at the same time would suggest there are still 7 books when you choose them? Hope that made sense.

 

[bloodysunday]

thats another problem: are the books taken at the same time, or one after the other?

 

[KungPow]

Well I've come to the conclusion the question sucks because it's too badly worded. But I remember my teacher telling me that if they don't say "without replacement" then you would assume that there's replacement. I'm not too sure still...

Can anyone help with the second Q?