SOLUTION: chris can mow the lawn in 2 hours and 23 minutes. Jim can mow the lawn in 3 hours and 15 minutes. If they work together, how long will it take them to mow the lawn. I tried to a

Algebra ->  Rate-of-work-word-problems -> SOLUTION: chris can mow the lawn in 2 hours and 23 minutes. Jim can mow the lawn in 3 hours and 15 minutes. If they work together, how long will it take them to mow the lawn. I tried to a      Log On


   

Question 577635: chris can mow the lawn in 2 hours and 23 minutes. Jim can mow the lawn in 3 hours and 15 minutes. If they work together, how long will it take them to mow the lawn. I tried to average the times but I got the answer wrong.
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Add their rates of mowing to get thir
rate working together
Chris's rate: ( 1 lawn ) / ( 2 hrs, 23 min )
Jim's rate: ( 1 lawn ) / ( 3 hrs 15 min )
Let +t+ = time in minutes for them
to mow lawn together
------------------
+2%2A60+%2B+23+=+143+
+3%2A60+%2B+15+=+195+
+1%2F143+%2B+1%2F195+=+1%2Ft+
Multiply both sides by +143%2A195%2At+
+195t+%2B+143t+=+143%2A195+
+338t+=+27885+
+t+=+27885%2F338+
+t+=+82.5+
+82.5+-+60+=+22.5+
Working together, it takes them 1 hr and 22.5 min
check:
+1%2F143+%2B+1%2F195+=+1%2F82.5+
+.006993+%2B+.0051282+=+.0121212+
+.0121212+=+.0121212+
OK