Binomial Probability (1 Viewer)

[Mainoyi]

A dental inspector finds that about 20% of children of a certain area have tooth decay. What is he probability that out of 6 children examined, only the first, third and fifth will have tooth decay?


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this is a question from 'fitz'
thanks!!!!

 

[Mainoyi]

Is this from Fitzpatrick? The question sounds familiar...

Anyways, i think it's like this:

6C3 X( 0.2)^3 X (0.8)^3
= 0.08192

yep,its from fitzpatrick
but that's not right...
the answer is 64/3125 (0.02048)

 

[Timothy.Siu]

Is this from Fitzpatrick? The question sounds familiar...

Anyways, i think it's like this:

6C3 X( 0.2)^3 X (0.8)^3
= 0.08192

thats wrong,read the question again

 

[Aerath]

Answer in Fitzpatrick is wrong if I remember correctly. I struggled over that for about 20 mins before finding out the next day that the answer was wrong. =\

 

[Trebla]

My guess is that you have to multiply the binomial probability by 1/2 because the probability of being in either 1st, 3rd or 5th position out of 6 positions is 1/2. For some reason the given answer multiplies it by 1/4 rather than 1/2....

 

[Timothy.Siu]

Actually, I got the answer now ^_^

This is a trick question, it doesn't involve C's at all. Because there are 3 out of the 6 who will have tooth decay that's : D, ND, D, ND, D, ND (D = decay, ND = no decay), then all you have to do is:

(0.2)^3 x (0.8)^3
= 0.004096

looks good

 

[Mainoyi]

Thanks guys..i get it now~~