time and work problem

X can do a piece of work in 2 hours, while Y can do the same piece of work in 4 hours.What is the time taken if X and Y do the work together?

converting to rate (quantity of work per unit time)

X can do (1/2) of the work in one hour
Y can do (1/4)th of the work in one hour

X+Y combined can do (1/2)+(1/4)=(3/4)th of the work in one hour

therefore X and Y combined will need 1 / (3/4)
or (4/3) hours to complete the work

that is 1 hour and 20 minutes

try the following page for some formulae time and work

other word problems with some explanation


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