Each week Manhattan GMAT posts a GMAT question on our blog and follows up with the answer the next day. Are you up for the challenge?
It takes Abby a hours to build a birdhouse. When Becky and Caroline help Abby, the three of them can build an identical birdhouse in half the time. If it takes Becky and Caroline b and c hours, respectively, to build a birdhouse on their own, which of the following statements is true?
A: 
B: 
C: 
D: 
E: 
