Sydney and Nathan are two of Santa's elves.

[idiotswithwordproblems]

Sydney and Nathan are two of Santa's elves. Sydney can make a toy in ten hours. Nathan can make the same toy in nine hours. How long would it take Sydney and Nathan if they were to make the toy together?

My answer is 9.5 hours. Is this correct?

 

[stapel]

My answer is 9.5 hours. Is this correct?

Nathan can do the job in nine hours. Why would it take him longer when he's getting help?

Please reply showing your work and reasoning. Thank you.

Eliz.

 

[tkhunny]

Sydney and Nathan are two of Santa's elves. Sydney can make a toy in ten hours. Nathan can make the same toy in nine hours. How long would it take Sydney and Nathan if they were to make the toy together?

My answer is 9.5 hours. Is this correct?

If both could do it in 10 hours, your method would produce 10? That's doesn't seem right. If you add a worker with similar abilities, you should get about half the time.

One way to think about these is a Least Common Multiple.

10 vs. 9 leads to 90

Sydney can make 9 in 90 hours.
Nathan can make 10 in 90 hours.
Together, that's 19 in 90 hours.
Calculate Hours / Toy.