John and David can finish a job together in 2 hours. If John can do the job by himself in 3 hours, what percent of the job does David do?
Select.
A) 36.33% B) 33.33% C) 39.33% D) 40.33% E) 33%
You can also plug in numbers. For example, Bob and Alice work at a donut factory and make 18 donuts which is the job ( I picked this as a SMART number).   John on his own works  18/3= 
<gadget id="calculator"> 18/3</gadget>
<output>6</output>
6 donuts per hour.   John and David work   18/2= 
<gadget id="calculator">  18/2</gadget>
<output>9</output>
9 donuts per hour so David works 3 donuts/hour   To find out the percentage, David works 3 donuts/hr x 2 hours= 6 donuts per hour.   Therefore 6 donuts/18donuts = 1/3 = 33.33%   Answer : 33.33%
<result>B</result>
John and David can finish a job together in 2 hours. If John can do the job by himself in 3 hours, what percent of the job does David do?