SOLUTION: A can do work in 12 Days,b in 6 days and c in 3 days.A and B start working together and after day,C jons them.The total numbers of days required to complete the work is ans:

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Question 780223: A can do work in 12 Days,b in 6 days and c in 3 days.A and B start working together and after day,C jons them.The total numbers of days required to complete the work is


ans:
a)16/7 b) 9/7 c)8/7 d)15/7

Found 2 solutions by josmiceli, lwsshak3:
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
What fraction of the job do A and B get done
working together?
Add their rates of working to get their rate
working together
A's rate: ( 1 job ) / ( 12 days )
B's rate: ( 1 job ) / ( 6 days )
C's rate: ( 1 job ) / ( 3 days )
Let +x+ = fraction of the job they do in 1 day
I can say:
+1%2F12+%2B+1%2F6+=+x%2F1+
+x+=+1%2F12+%2B+2%2F12+
+x+=+3%2F12+
+x+=+1%2F4+
-------------------
They complete +1%2F4+ of the job, so there is
+3%2F4+ left to do
Now with all 3 working, let +t+ = days
to complete the job
+1%2F12+%2B+1%2F6+%2B+1%2F3+=+%283%2F4%29%2Ft+
+1%2F12+%2B+2%2F12+%2B+4%2F12+=+9%2F%2812t%29+
Multiply both sides by +12+
+1+%2B+2+%2B+4+=+9%2Ft+
+7+=+9%2Ft+
+t+=+9%2F7+
1 day has already been spent, so the total days worked is
+7%2F7+%2B+9%2F7+=+16%2F7+
(a) 16/7 answer
-------------
check:
+1%2F12+%2B+1%2F6+%2B+1%2F3+=+%283%2F4%29%2Ft+
+1%2F12+%2B+2%2F12+%2B+4%2F12+=+%283%2F4%29+%2F+%289%2F7%29+
+7%2F12+=+%287%2F9%29%2A%283%2F4%29+
+7%2F12+=+7%2F12+
OK

Answer by lwsshak3(11628) About Me  (Show Source):
You can put this solution on YOUR website!
A can do work in 12 Days,b in 6 days and c in 3 days.A and B start working together and after day,C jons them.The total numbers of days required to complete the work is
***
let x=number of days required to complete the work
A's work rate=1/12
B's work rate=1/6
C's work rate=1/3
x%2F12%2Bx%2F6%2B%28x-1%29%2F3=1
LCD:12
x+2x+4x-4=12
7x=16
x=16/7
ans: a)