A worker can load one truck in 6 hours. A second worker can load the same truck in 4 hours. If both workers load one truck simultaneously while maintaining their constant rates, how long, in hours, will it take them to fill one truck?
Choose the correct answer:
A) 2.1
B) 2.4
C) 2.7
D) 3.0
E) 3.3

Rationale: the workers fill the truck at a rate of 1 / 6 + 1 / 4 = 10 / 24 = 5 / 12 of the truck per hour . then the time to fill one truck is 12 / 5 which is 2.4 hours . the answer is b .
Answer: B