1.

X And Y Can Do A Piece Of Work In 20 Days And 12 Days Respectively. X Started The Work Alone And Then After 4 Days Y Joined Him Till The Completion Of The Work. How Long Did The Work Last ?

Answer»

X ONE day work = 1/20

y one day work = 1/12

work done by x in 4 DAYS = 4 * 1/20 = 1/5

left work = (1-1/5) = 4/5

 x and y one day work = (1/20 + 1/12) = 8/60 = 2/15

=> time required to do 2/15 PART of work by x and y = 1 day 

so for WHOLE work = 1/(2/15) = 15/2

so for 4/5 part of work x and y will take =( 4/5*15/2 ) = 6 days. 

=> How long did the work LAST = 4 day + 6 day = 10 days.

X one day work = 1/20

y one day work = 1/12

work done by x in 4 days = 4 * 1/20 = 1/5

left work = (1-1/5) = 4/5

 x and y one day work = (1/20 + 1/12) = 8/60 = 2/15

=> time required to do 2/15 part of work by x and y = 1 day 

so for whole work = 1/(2/15) = 15/2

so for 4/5 part of work x and y will take =( 4/5*15/2 ) = 6 days. 

=> How long did the work last = 4 day + 6 day = 10 days.


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