Question

one printer can do a printing job in 2hr. Another printer can do the same job in 8hr. How long does it take the two to do the job together?

Answer 1

\[\frac{8\times 2}{8+2}\]
\[\frac{16}{10}=1.6\]

Answer 2

the answers to choose from are 1&5/11hr 1&3/5hr 2&2/3hr or 1/10hr

Answer 3

1.6 is one and three fifths

Answer 4

As you can see from sat's answer, there is a simple formula to solve these types of problems.

Hopefully you can just learn it. But here is a way to do the problem that might help?

when they say a printer does a job in 2 hours, you can think of it as 1 job per 2 hours, or
1/2 job per hour.

If you multiply by the number of hours it works, you get the number of jobs it does. For example, 1/2 job per hour times 2 hours = 1 job.

With 2 printers, working together, where one does 1/2 job per hour, and the other does 1/8 job per hour, we find the number of jobs by adding:

1/2 * t + 1/8 * t = # of jobs

Here t is the number of hours they print. Of course, you want just 1 job. so

1/2 t + 1/8 t = 1

can you solve for t? Put them over a common denominator 8:
4/8 t + 1/8 t = 1
5/8 t =1
t = 8/5 hour

change 8/5 hour to 1 and 3/5 hour or 1 hour 36 minutes