Question

12.

Future Electronics makes compact disc players. Its research department found that the life of the laser beam device is normally distributed, with mean 5460 hours and standard deviation 470 hours 

(a) Find the probability that the laser beam device will wear out in 5000 hours or less. 

(b) Future Electronics wants to place a guarantee on the players so that no more than 10% fail during the guarantee period. Because the laser pickup is the part most likely to wear out first, the guarantee period will be based on the life of the laser beam device. How many playing hours should the guarantee cover? 

13.

Suppose 25% of the area under the standard normal curve lies to the left of z. Is z positive or negative? 

Answer 1

q-12)

Given data:

mean life,

Standard deviation

a)

probability for laser beam device will wear out in 500o hrs or less. P(x<=5000 hrs.)

Z(5000 hrs)=-0.98

from normal distribution table.

P(x<=5000)= 0.16354

probability for laser beam device will wear out in 500o hrs or less is 0.16354

b)

gurantee hour for return should be less than 10% = X

Z value for 10% from normal distribution table.

Z(0.10027)=-1.28

Z(0.09853)=-1.29

Z(0.10)=-1.2816

X=4857.648hrs.

guarantee period of laser beam device have to return should be not more than 10% is 4857.648 hrs

Q-13)

Z value below 50% is negative and more than 50 % is + ve.

so z value for 25% is negative

option is Negative