Answer:
60%
Step-by-step explanation:
if 450 = 100%
what about 270?
720-450=270
300/15=20 hours
Hope this helps! :)
Answer:

Step-by-step explanation:
The area of a trapezoid.





Answer:
Step-by-step explanation:
given that certain tubes manufactured by a company have a mean lifetime of 800 hours and a standard deviation of 60 hours.
Sample size n =16
Std error of sample mean = 
x bar follows N(800, 15)
the probability that a random sample of 16 tubes taken from the group will have a mean lifetime
(a) between 790 and 810 hours,
=
(b) less than 785 hours

, (c) more than 820 hours,

(d) between 770 and 830 hours
=