Barry can do a certain job in 3 hours, whereas it takes Sanchez 7 hours to do the same job. How long would it take them to do the job working together?

Question

Equation isn't clear

Answer 1

Barry: 1/3 job per hour

Sanchez : 1/7 job per hour

 

1/3 + 1/7 = 10/21 jobs per hour is their combined speed.

 

10/21 jobs          1 job

------------   =   --------------

  1 hour               ? hour

 

10/21 * ? = 1

 

? = 21/10 = 2 and 1/10  hours = 2 hours and 6 minutes, because 1/10 hr = 60/10 minutes = 6 min

 

 

Answer 2

1/3 + 1/7 = 1/t

 

t = the amount of time it would take the two of them to do the job working together.

 

7t + 3t = 21

10t = 21

t = 21/10 = 2.1 hours