Question

Jack can complete autumn - cleaning in a house in 7 hours. Cindy can complete autumn - cleaning in the same house in 5 hours. If Jack works for 1 hour alone and then Cindy joins Jack to finish the autumn cleaning, what is the total time it takes to complete the autumn - cleaning? A. 3 hours, 30 minutes
B. 3 hours 15 minutes
C. 2 hours, 30 minutes
D. 2 hours, 15 minutes
E. 2 hours, 20 minutes
Jawabannya adalah A tetapi caranya bagaimana?