Explanation:
When Joe works alone, the total number of words he typed can be given by:
Total words = (40 words per minute) x (60 minutes per hour) x (2.5 hours)
Total words = 6000 words
Now, when Joe and Mark work together, let 'y' be the number of hours for which they both work simultaneously:
Total words = Words Typed by Joe + Words Typed by Mark
6000 = {(40 words per minute) x (60 minutes per hours) x (y hours)} + {(20 words per minute) x (60 minutes per hours) x (y hours)}
6000 = 2400y + 1200y = 3600y
y = 1.67 hours = 1 hour and 40 minutes
Thus, working together simultaneously, Joe and Mark will take 1 hour and 40 minutes to complete the report.
