thank you for your reply . :)
But i am not able to do question 1????????
Please help me with these probability questions
1. A manufacturer of small electric motors wishes to give a guarantee on all those motors that fail prematurely, but does not want to replace too many motors. If the lifetimes fo the electric motors are normally didtributed with a mean of 8 years and a standard deviation of 2 years, what guarantee should be offered so that not more than 5% of the motors are replaced?????
2. A normal distribution has mean 20 and standard deviation=3. If X is the mean of a random sample of size 49 taken from this diatribution then determine the following
a) P(18<X<22)
b) P(X>19.5)
c) P(X<21)
d) The number 'k' such that P(20-k<X<20+k) = 0.90
3. The weights fo ball bearings are normally distributed with mean 0.614 and standard deviation of 0.003
Determine the percentage of ball bearings with weights:
a) between 0.610 and 0.618
b) greater than 0.616
c) less than 0.607
d) Determine the new mean with standard deviation fixed so that the answer to question (b) is 25%
4. A small hire has three cars which it hires out by the day. Records show that the mean demand over the day is 2.7 cars per day. If it is assumed that the demand for cars follows a poisson distribution determine
the percentage of days on which
a) no cars are hired
b) 2 or 3 cars are hired
c) Demand outstrips the supply
d) IF the firm buys another car for hire determine the percentage reduction in the answer for question (c)
I GOT ANSWER FOR QUESTION 4 AS
a) 6.7%
b)46.5%
c)28.6%
d)13.73%
PLEASE TELL ME WHETHER THE ANSWER I GOT FOR QUESTION 4 IS CORRECT OR NOT
PLEASE ALSO TELL ME HOW TO SOLVE THE FIRST THREE PROBLEMS
THANKS SO MUCH IN ADVANCE
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