John and David can finish a job together in 1 hours. If John can do the job by himself in 2 hours, what percent of the job does David do?	Answers:
A) 40%
B) 45%
C) 50%
D) 55%
E) 60%
You can also plug in numbers. For example, Bob and Alice work at a donut factory and make 10 donuts which is the job ( I picked this as a SMART number).   John on his own works  10/2= 
<gadget id="calculator"> 10/2</gadget>
<output>5</output>
5 donuts per hour.   John and David work   10/1= 
<gadget id="calculator">  10/1</gadget>
<output>10</output>
10 donuts per hour so David works 5 donuts/hour   To find out the percentage, David works 5 donuts/hr x 1 hours= 5 donuts per hour.   Therefore 5 donuts/10donuts = 1/2 = 50%   Answer : 50%
<result>C</result>
John and David can finish a job together in 1 hours. If John can do the job by himself in 2 hours, what percent of the job does David do?