Answer:
0.83
Step-by-step explanation:
(a) z = (x - mean) / sd = (4000 - 3750) / 300 = 0.83
This corresponds to 0.7967 from the z-table, which represents how many last less than 4000 hours, so the answer is 1 - 0.7967 = 0.2033
(b) It will be P(x<4000) - P(x>3600) = 0.7967 - whatever the corresponding value is.
(c) same procedure as (b).
(d) 2% above corresponds to 0.02 which is a z-score of -2.05
-2.05 = (x - 3750) / 300
x = 3135
