The mean is not the same thing as median
mean=78+81+85+87=331
mean=331/4=82.75
median is the middle number, but you have a par set of numbers, so your median will be the middle numbers 78,81,85,87 , which are 81+85=166, 166/2=83
83 is your median
Answer: C.-1.5
Step-by-step explanation:
Given: The burning time of a very large candle is normally distributed with mean
of 2500 hours and standard deviation
of 20 hours.
Let X be a random variable that represent the burning time of a very large candle.
Formula: 
For X = 2470

So, the z-score they corresponds to a lifespan of 2470 hours. =-1.5
Hence, the correct option is C.-1.5.
^ You again? Quit being sus and answer the question here instead of elsewhere.
To find the mean, all you have to do is add each number and then divide by how many numbers you added.
So, 38 + 29 + 16 + 42 + 33 = 158. There were five numbers added, so the next step is to divide 158 by 5. That equals 31.6 as your answer.