John and David can finish a job together in 4 hours. If John can do the job by himself in 5 hours, what percent of the job does David do?  Select
A) 20%	B) 25%	C) 24%	D) 23%	E) 22%
You can also plug in numbers. For example, Bob and Alice work at a donut factory and make 20 donuts which is the job ( I picked this as a SMART number).   John on his own works  20/5= 
<gadget id="calculator"> 20/5</gadget>
<output>4</output>
4 donuts per hour.   John and David work   20/4= 
<gadget id="calculator">  20/4</gadget>
<output>5</output>
5 donuts per hour so David works 1 donuts/hour   To find out the percentage, David works 1 donuts/hr x 4 hours= 4 donuts per hour.   Therefore 4 donuts/20donuts = 1/5 = 20%   20%nswer : 20%
<result>A</result>
John and David can finish a job together in 4 hours. If John can do the job by himself in 5 hours, what percent of the job does David do?