Question

At a telephone enquiry system the number of phone calls received regarding relevant inquiry follows probability distribution with an average of 5 phone calls during 10 minute time interval. The probability that there is at the most one phone call during a 10 minute period is___

• A. $\frac{5}{e^{-5}}$
• B. $\frac{5}{e^5}$
• C. $\frac{6}{e^{-5}}$
• D. $\frac{6}{e^5}$

Answer 1

The correct option is D $\frac{6}{e^5}$

$P(X=r)=\frac{e^{-m}{m}^r}{r!}$
$P(X\le 1)=P(X=0)+P(X=1)$
$=e^{-5}+5\times e^{-}5=\frac{6}{e^5}$