College Algebra
posted by Devin .
Charlie can grade exams in 2 hours. It takes Mark 6 hours to grade the same exams. If they work together, how long will it take for them to grade the exams?

I figured it out. 40 minutes. Thanks anyway

1/T = 1/2 + 1/6,
1/T = 3/6 + 1/6,
1/T = 4/6 = 2/3,
T = 3/2 = 1.5HRS. 
Angela cam comlete a project in 2 hours. it takes Jason 3 hours to complete the same project. how long will it take for them to complete the project together?