SOLUTION: heres the question i need help with please. The Key Refining Company, referred to earlier, determined that 20% of its customers do not pay their bill by the due date. What is t

Question 423444: heres the question i need help with please.
The Key Refining Company, referred to earlier, determined that 20% of its customers do not pay their bill by the due date. What is the probability that for a sample of 80 customers, less than 18 will not pay their bill by the due date?
Can you use the normal approximation to the binomial on this problem? Why or why not? What constraints must be met?

My theory is no normal curve i solved this by using
p=80
80 (.80)plus or minus 5
80 (.20) plus or minus 5
am i close?????

Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
The Key Refining Company, referred to earlier, determined that 20% of its customers do not pay their bill by the due date. What is the probability that for a sample of 80 customers, less than 18 will not pay their bill by the due date?
Can you use the normal approximation to the binomial on this problem? Why or why not? What constraints must be met?
Check:
np >= 5 ; np >= 5 ?
80(0.20) = 16
80(0.80) = 64
--
So you could use the normal approximation.
---
If you do you get the following:
z(17.5) = (17.5-16)/sqrt(16*0.8) = 0.4193
P(x < 18) = P(z< 0.4193) = 0.5525
=====================================
Cheers,
Stan H.
=============
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