Question 439886
<pre><font face = "Tohoma" size = 4 color = "indigo"><b> 
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 = blue(x - mu)/blue(sigma)}}}
   z = (440-500)/100 = -.6
 P(z > -.6) = 1 -  NORMSDIST(-.6)= 1 - .2743 = .7557  OR 75.57%
{{{drawing(400,200,-5,5,-.5,1.5, graph(400,200,-5,5,-.5,1.5, exp(-x^2/2)), green(line(-.6,0,-.6,exp(-.6^2/2))),locate(4.8,-.01,z),locate(4.8,.2,z))}}}