*THIS IS AN ANSWER BECAUSE I CAN'T ANSWER SOMEONE'S QUESTION*
Bob can do a job in 5 hours, while Bill can do the same job in 8 hours. How many hours would it take them, working together, to do this job?

ANSWER:

The one in the following equation stands for ONE WHOLE JOB.

[tex]\frac{1}{5}x+\frac{1}{8}x=1\\\\[/tex]

[tex]x=\frac{40}{13} hours[/tex]

hence, this is the answer.