SOLUTION: 10 Men begin to work together on a job, but after some days, 4 of them left the job. As a result the job which could have been completed in 40 days is completed in 50 days. How m

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Question 596105: 10 Men begin to work together on a job, but after some days, 4 of them left the job. As a
result the job which could have been completed in 40 days is completed in 50 days. How
many days after the commencement of the work did the 4 men leave?
(a) 25 (b) 30 (c) 10 (d) 15

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
This says that 10 men could have done the job
in 40 days.
1 man would have taken 10 times as long, so
1 man does the job in 400 days
Let +n+ = number of days after start when 4 men leave job
+50+-+n+ = number of days after 4 men leave
-----------------
In general, ( rate of working for 1 man ) x ( number of men ) x ( number of days ) = part of job completed
( 1 job / 400 days ) x ( 10 men ) x ( n days ) = part of job completed
( 1 job / 400 days ) x ( 6 men ) x ( 50 - n days ) = part of job completed
The 2 parts add up to 1 job completed
-----------------
+%28+1%2F400+%29%2A10n+%2B+%28+1%2F400+%29%2A6%2A%28+50+-+n+%29+=+1+
+%28+1%2F400+%29%2A%28+10n+%2B+300+-+6n+%29+=+1+
+4n+%2B+300+=+400+
+4n+=+100+
+n+=+25+
+50+-+n+=+50+-+25+
+50+-+n+=+25+
The 4 men left 25 days after the work started
check:
+%28+1%2F400+%29%2A10n+%2B+%28+1%2F400+%29%2A6%2A%28+50+-+n+%29+=+1+
+%28+1%2F400+%29%2A10%2A25+%2B+%28+1%2F400+%29%2A6%2A%28+50+-+25+%29+=+1+
+250%2F400+%2B+%28+6%2A25+%29+%2F+400+=+1+
+250+%2B+150+=+400+
+400+=+400+
OK