What are the symbols for this formula? Thanks. There is no explanation given on the Web site where I found the answer.

The answer is .223

1.A catalog company that receives the majority of its orders by telephone conducted a study to determine how long customers were willing to wait on hold before ordering a product. The length of time was found to be a random variable best approximated by an exponential distribution with a mean equal to 3 minutes. What proportion of customers having to hold more than 4.5 minutes will hang up before placing an order?

Answer

Question 9 answers

0.77687

0.51342

0.22313

0.48658