The lifetime of lightbulbs are normally distributed with Mean = 8,097 hours and SD = 58 hours, If we want to be sure that 95% of all bulbs last longer than the advertised figure, what figure should be advertised?

(Tips This is to ask you to find a particular x-value so that P(X > x-value) = 0.95 or very close;

This can be converted as: P(Z > (x-value - µ)/σ) ) = 0.95.

Tip: Draw the normal chart. Now you divide the whole curve with one side (left side) is only 5% and the right side is 95%. What is the Z-value?