Richie and his brother have a paper route. Together they can deliver all of the papers in 40 minutes, and Richie can do it alone in 90 minutes. Richie’s brother slept in one day, leaving Richie to deliver alone for 30 minutes. How long must the two of them work together to finish delivering the newspapers?

approximately 26.66667  minutes

This converts to 26 minutes, 40 seconds

Explanation:

Let's say there are 360 newspapers that need to be delivered.

The two brothers can get the job done in 40 minutes if they work together. Their rate is 360/40 = 9 newspapers per minute.

Richie can do the full job alone in 90 minutes. So his rate would be 360/90 = 4 newspapers per minute. In 30 minutes, he delivers 30*4 = 120 newspapers. This leaves 360 - 120 = 240 left over.

Divide this over the rate of 9 papers per minute to get 240/9 = 26.66667 approximately. It takes about 26.66667 minutes to finish up delivering the 240 remaining newspapers if the brothers work together.

The portion 0.66667 multiplies with 60 to get 0.66667*60 = 40.0002 which rounds to 40 (we have rounding error going on). This means

26.66667 minutes = 26 minutes, 40 seconds

78.59 is the mean

step-by-step explanation: