SOLUTION: A light bulb has an average life of 500 hours with a std. deviation of 100 hours. This can be approx. by a normal distr. curve. An amusement park buys and installs 10,000 of such b

Question 439886: A light bulb has an average life of 500 hours with a std. deviation of 100 hours. This can be approx. by a normal distr. curve. An amusement park buys and installs 10,000 of such bulbs. Find the total number than can be expected to last for:

a) Less than 500 hours
b)more than 440 hours
Answer by ewatrrr(24785) (Show Source): You can put this solution on YOUR website!

 

Hi

A light bulb has an average life of 500 hours with a SD = 100 hours.

amusement park buys and installs 10,000 of such bulbs.

 Number lasting <500hr: 50% of them OR 5,000

 Number lasting more than 440 hours = .7557*10,000 = 7,557 

*Note: 

   z = (440-500)/100 = -.6

 P(z > -.6) = 1 -  NORMSDIST(-.6)= 1 - .2743 = .7557  OR 75.57%

 

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