Sandy can do a job in 18 days and Molly can do the same job in 36 days. If they work together, in how many days will they complete the job?  Choose the correct choice from the following answers.
A) 6	B) 8	C) 10	D) 12	E) 15
Sandy can do 1/18 of the job each day.   Molly can do 1/36 of the job each day.   The combined rate is 1/18 + 1/36 = 1/12 of the job each day.   The job will take 12 days.   The answer is 12.
<result>D</result>
Sandy can do a job in 18 days and Molly can do the same job in 36 days. If they work together, in how many days will they complete the job?