Worker a works at a constant rate and, working alone, can complete a job in 6 hours. worker b works at a constant rate and, working alone, can complete the same job in 5 hours. worker c works at a constant rate and, working alone, can complete the same job in 3 hours.

So then we will have that the 3 working together will complete 1 job in approximately 1.429 hours for this case.

Explanation:

If we want to express the situation in math terms and find the number of hours that takes to complete 1 job with the 3 at the same time, we can do this.

For this case we have the following rates:

And we know that working together the rate would be the addition of the rates like this:

And if we divide the numerator and denominator by 7 we got:

So then we will have that the 3 working together will complete 1 job in approximately 1.429 hours for this case.