<span>Let us first find a ratio between the quantity of work done by Darnell and Julius. If Darnell does one part of the work, Julius does two parts of the work. That is, their work quantity ratio is 1:2. (Total 3 parts) In other words when Darnell does 1/3 of the work, Julius does 2/3 of the work.
When they work together, the work is completed in 4 hours. 4 hours work is the combined output of 1/3 by Darnell and 2/3 by Julius. If Julius was not there, Darnell would have to work for more than 4 hours.
We already know that Darnell does only 1/3 of a work during any given time. If the given time is 4 hours, how many one-thirds will Darnell require? To find the answer, divide the given number (4 hours in this case) by the given fraction( 1/3 in this case) To divide a number by a fraction, multiply the number by the reciprocal of the fraction. Thus it becomes 4 divided by 1/3 = 4 x 3/1 = 12.
(Another hint: At the rate of 1/3 of a work in one hour, Darnell will needs 3 hours to complete the given task. If the given work is 4 hours long, Darnell will take 4 x 3 hours, that is 12 hours.)</span>
