ap stat question on college board help!

slipstream99
Wed, 04 May 2005 07:29:16 +0000

Number 1: Make a probability tree.

All bags (p=1)
…Forbidden material (p=.001)
…Triggers (p=.97)

…Not Forbidden (p=.999)
…Triggers (p=.15)

So, the probability that forbidden material will actually be detected is (.97)(.001) = .00097. The probability that not forbidden material will be detected asa forbidden is (.999)(.15) = .14985.

.00097/(.14985+.00097) = .0064.

Number 2:
Group weight = 190*4 = 760
Group Standard Deviation of weight = sqrt[(10^2)(4)] = 20
normalcdf(800,10^10,760,20) = .0227.

You have to square standard deviation of each subject, add them together, then take the square root to get standard deviation of them all together.

Number 3:
This one doesn’t make sense to me since (4^2)(10) = 160 and (40^2)(10) = 16000, not 1600. Regardless, since it seems that you’re missing 64 (1664-1600), you probably forgot to use the box’s standard deviation when calculating total standard deviation.