X= entire test
if
18=.9x
then divide both sides by .9
18/ .9
and x = 20
20 questions total on the test
Answer:
15.87%
Step-by-step explanation:
Given that:
The mean (μ) = 1000 hours, the standard deviation (σ) = 100 hours.
The z score provides a means of measurement in statistics to determine the variation of a raw score from the mean. The z score is given as:

To find that a randomly chosen light bulb will last less than 900 hours:

Therefore, P(x < 900) = P(z < -1) = 0.1587 = 15.87%
Answer:
yes but y do u ask?
Step-by-step explanation: