One robot builds a robot in 1 hour, another one builds a robot in 2 hours. The 2 robots work together and when a new robot is complete, it joins the others, working at a constant rate of one robot in 2 hours. How much time will it take until there are 3 robots altogether, if the robots build only one robot at a time?  Choose the correct choice from the following choices:
A) 40 min  B) 94 min  C) 110 min  D) 112 min  E) 120 min
First the 2 robots work at the rate of   1 + 1/2 = 3/2   so they complete one robot in 2/3 rd of an hour = 40 minutes - (1)   40 minnd now we have 3 robots in 40 minutes   40 minnswer -40 min
<result>A</result>
One robot builds a robot in 1 hour, another one builds a robot in 2 hours. The 2 robots work together and when a new robot is complete, it joins the others, working at a constant rate of one robot in 2 hours. How much time will it take until there are 3 robots altogether, if the robots build only one robot at a time?