Mr. Pollob can do a job in 120 minutes, while his colleague can do the same job in 3 hours. How long will it take them to work together to finish the same job?

Question: Mr. Pollob can do a job in 120 minutes, while his colleague can do the same job in 3 hours. How long will it take them to work together to finish the same job?

Solution:
Mr. Pollob can do a job in 120 minutes = 2 hours
∴ Mr. Pollob can do in 1 hour = 1/2 portion of the job

His colleague can do in 1 hour = 1/3 portion of the job

Together they can do in 1 hour = 1/2 + 1/3 = 5/6 portion of the job

∴ Together they can do full job in (6/5) hour = (6 × 60)/5 minutes
= 72 minutes