Trying to solve this with my ti 89 can someone help ???In one county, the conviction rate for DUI is 85%. Estimate the probability that of the next 100 DUI summonses issued, there will be at least 90 convictions.

Question

amistre64 · Answer

is this a normal distribution?  do we assume a mean of 0 and and sd of 1?

anonymous · Answer

yes it is.

anonymous · Answer

i have solved several like this i just need help getting started again

amistre64 · Answer

"the next 100" sounds more like a Poisson distribution to me .....

anonymous · Answer

Estimate the indicated probability by using the normal distribution as an approximation to the binomial distribution

anonymous · Answer

would it be a binomial cdf ??

amistre64 · Answer

it could be, but they seems to want the normal approximation to it instead

anonymous · Answer

hmmmmm

amistre64 · Answer

success is .85 right?
fail is then .15

amistre64 · Answer

and the term "at least" is important

anonymous · Answer

that would be  90 or more

amistre64 · Answer

yes, and our sample size n is 100

anonymous · Answer

i have the ti 89 calc. with the stats list editor app i know it can solve this

amistre64 · Answer

i never got fancy enough to play on a ti89; my class used the ti83

amistre64 · Answer

mean = n*success;  mean = 85 in this case

amistre64 · Answer

and sd = sqrt(n*success*fail)

sqrt(85*.15) = sqrt(12.75) = 3.571

amistre64 · Answer

i think the rest is just using the normalCDF function now

amistre64 · Answer

or just plug those right into the normalCDF

nCDF(low, high, mean, sd)
        (90,9999,100*.85,sqrt(100*.85*.15))

anonymous · Answer

so standard deviation is 3.571

amistre64 · Answer

i recall some caveat about making it a halfway point for the low or high tho to lessen the error

amistre64 · Answer

the function will work out the math for you if you just plug in the mathing :)

anonymous · Answer

i put from 90 to infinity

amistre64 · Answer

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