Help in solve this question...

Can anyone please help me solve this Question from
Quantitaive Section in GRE

Ques : A lion can eat a sheep in 2 hrs, wolf in 3 hrs,
and a dog in 6 hours. In what time would they eat a
sheep together?

Answer options :
a. 60 mins b. 75 minutes c. 52 minutes d. 55 minutes

The right answer is 52 minutes

Regards
Nandu

l=1/2 sheep/hour
w=1/3
d=1/6

1/2+1/3+1/6 = 1 sheep/hour

So, I get:

a. 60 minutes

Thats what I think. But just wanted to check w/ you mathe geniouses .
I guess the answer in the exam was wrong or something.

Thanks
Nandu

And I get:
Lion can eat 1 sheep in 2 hours, or 3 sheep in 6 hours
Wolf can eat 1 sheep in 3 hours, or 2 sheep in 6 hours
Dog can eat 1 sheep in 6 hours

So, together, they can eat 6 sheep in 6 hours, or, 1 sheep in 1 hour.