Algebraic Expressions

Question

Jericho can finish a computer graphics job twice as fast as Clarence, working together, it takes them 5 hrs, how long would it take Jericho to finish the job alone? 

Answer 1

1/J + 1/C = 1/5

1/(C/2) + 1/C = 1/5

2/C + 1/C = 1/5

multiply by 5C

10 + 5 = C

C = 15 hours to complete the job alone for Clarence

J =C/2 = 7.5 hours to complete the job alone for Jericho

1/7.5 + 1/15 = 1/5

multiply by 15

2 + 1 = 3