Customers arrive at the cashier desks at a grocery store randomly with an average rate of 31 per hour. (Assume CVa=1.) Each cashier works at a different speed, so it takes on average 1.36 minutes to scan items and process payment. (Assume CVp=1.) The grocery store considers two queue designs.

The first option is to have customers line up separately in front of 2 cashiers; this is called independent queueing.

The second option is to have a single line leading up to 2 parallel cashiers; this is called pooled queueing.

How long do customers wait on average before a cashier starts scanning/payment in the pooled queueing option?