The life expectancy of a typical lightbulbis normally distributed with a mean of 4000 hours and has a standard deviation of 42 hours/ what is the probability that a lightbulb will last between 3,875 and 4055 hours?
A.8835
B.7825
C.9133
D.9035

Question

The life expectancy of a typical lightbulbis normally distributed with a mean of 4000 hours and has a standard deviation of 42 hours/ what is the probability that a lightbulb will last between 3,875 and 4055 hours?
A.8835
B.7825
C.9133
D.9035

amistre64 · Answer

what are your ideas on how to proceed?

amistre64 · Answer

also, do you have a table to use, or can you work this with a ti83 stats calculator?

anonymous · Answer

I'm not too sure, i tried to figure it out in my calculator but i cant seem to do it right. Would you mind helping me?

amistre64 · Answer

what type of calculator?

anonymous · Answer

I have my phone calculator and any one on the web, but i think i have a ti83 around my house somewhere

amistre64 · Answer

a ti83 is simple if its handy.  otherwise we could use the wolf

anonymous · Answer

sorry i have no idea where it is, you mind if we use wolfram?

amistre64 · Answer

the wolf works .. we want to use a normalcdf function since we want to find the cumulative probability ... an area under the curve, the format is: normalcdf(low, high, mean, sd) http://www.wolframalpha.com/input/?i=normalcdf%283875%2C4055%2C4000%2C42%29

amistre64 · Answer

it tells us the inner z, is about .9034

anonymous · Answer

and the inner z is the probability the lightbulb will last between 3,875 and 4055 hours?

amistre64 · Answer

yes

anonymous · Answer

Wow thanks for the help man, really saved me. Anyway you could help me with another?

amistre64 · Answer

maybe one more

anonymous · Answer

cool thanks

anonymous · Answer

the function f(t)=3 cos( (pi/6)t)+5 represents the tide in blastic sea. it has a maximum of 8 feet when time (t) is 0 and a minimum of 2 feet. The sea repeats this cycle every 12 hours. After nine hours, how high is the tide?
A 12 feet
B 5 feet
C 4.5 feet
D 2.5 feet

amistre64 · Answer

find f(9)

amistre64 · Answer

when t = 9 ,,, 3 cos(9pi/6)+5 http://www.wolframalpha.com/input/?i=3+cos%289pi%2F6%29%2B5

anonymous · Answer

So that gives me 5 feet as a result correct?

amistre64 · Answer

yep

amistre64 · Answer

from stats to trig ... what type of assessment are you taking?

anonymous · Answer

Thanks for the help man, big help.
I always see people giving medals, is there a way i can give one to you?

anonymous · Answer

Its an algebra 2 course, but its the getting into trig section.

amistre64 · Answer

there should be a 'best response' button on everything i post.  if you dont see it, try refreshing your browser.

anonymous · Answer

Yea i did give you that,is that the medal?

amistre64 · Answer

it is

anonymous · Answer

Ok, Thanks for all the help really appreciate it

amistre64 · Answer

youre welcome, and good luck :)