Note: You'll need the Normal Distribution Table. A certain type of light bulb has a lifetime in hours which is normally distributed with mean μ=650 and standard deviation σ=40. What is the probablility that a randomly selected light bulb has a lifetime in the range (700, 850)? Now this is how I tried to do this: We have to find P(700 ≤ X ≤ 850), but we need it in terms of Z. Now, Z= (X-μ)/σ Z= (X-650)/40 But we have to apply this to all the sides of the inequality, so we end up with P(1.25 ≤ (X-650)/40 ≤ 5) = P(1.25 ≤ Z ≤ 5) But using the Normal Distribution Table, there is no probability for the "5" bit of the inequality. So I'm not sure how to do this. Thanks.