Please answer these questions. I am in dire need of the answers... thanks


1.)Suppose daily sales follow an unknown probability distribution with a population mean of $9000 and a population standard deviation of $1500. What is the probability that any randomly chosen day would have a sales level of:

a) At least $5250 but no more than $12750?
b) Between $4000 and $14,000?
Suppose it was known that daily sales followed a bell curve: Then what is the probability that on any given day sales would be:
c) Between $7500 and $10,500?
d) Greater than $12,000?

I will do part a. That ought to allow you to do the others.

Do you have a stats book with the standard normal table? The z-table?

z=\frac{x-{\mu}}{\sigma}

z=\frac{5250-9000}{1500}=-2.5

z=\frac{12750-9000}{1500}=2.5

The z-scores are -2.5 and 2.5. That means you are 2.5 standard deviations on either side of the mean.

Look up those values in the table and we see for -2.5 we get 0.0062

For 2.5 we get 0.9938

Since you want in between those values, subtract them

0.9938-0.0062=0.9876

There is almost a 99% probability of falling between those values.