SOLUTION: solve. Round to the nearest tenth of necessary Mr. Jansen can shingle a roof in 10hrs, and Mr. Doyle can do it in 8 hrs. Mr. Davies has never done the job alone; but last time

Algebra ->  Rate-of-work-word-problems -> SOLUTION: solve. Round to the nearest tenth of necessary Mr. Jansen can shingle a roof in 10hrs, and Mr. Doyle can do it in 8 hrs. Mr. Davies has never done the job alone; but last time      Log On


   



Question 1034413: solve. Round to the nearest tenth of necessary

Mr. Jansen can shingle a roof in 10hrs, and Mr. Doyle can do it in 8 hrs. Mr. Davies has never done the job alone; but last time he helped with a similar job, it took the three men 3 1/3 hrs working together. How long would it take Mr. Davies alone?

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Add their rates of working to get
their rate working together
Mr. Jansen's rate:
[ 1 roof ] / [ 10 hrs ]
Mr. Doyle's rate:
[ 1 roof ] / [ 8 hrs ]
The 3 men working together:
[ 1 roof ] / [ 3.5 hrs ]
----------------------------
Let +t+ time in hrs for Mr. Davies to
shingle the roof working alone
+1%2F10+%2B+1%2F8+%2B+1%2Ft+=+1%2F3.5+
+1%2F10+%2B+1%2F8+%2B+1%2Ft+=+2%2F7+
Multiply both sides by +7%2A8%2A10t+
+56t+%2B+70t+%2B+560+=+2%2A80t+
+126t+%2B+560+=+160t+
+34t+=+560+
+t+=+16.4706+ hrs
and
+.4706%2A60+=+28.2353+
-------------------------
Working alone, Mr Davies takes 16 hrs 28 min
-------------------------
check:
+1%2F10+%2B+1%2F8+%2B+1%2F16.4706+=+1%2F3.5+
+.1+%2B+.125+%2B++.06071+=+.28571+
+.225+%2B+.06071+=+.28571+
+.28571+=+.28571+
OK