If A can fill a tank in 10 hours and B in 8 hours, how long will it take if both work together?

4 hours 30 minutes

5 hours

4 hours 26 minutes

4 hours 48 minutes

A’s 1 hour work = 1/10

B’s 1 hour work = 1/8

Combined work per hour = 1/10 + 1/8 = (4 + 5)/40 = 9/40

Time = 1 ÷ (9/40) = 40/9 ≈ 4.44 hours = 4 hours 48 minutes