John can clear a lot in 1.5 hours. His partner can do the same job in 4.5 hours. How long will it take them to clear the lot working together?

1.125 h = 1h 7.5 min = 1 h 7 min 30 sec

Step-by-step explanation:

John makes 1/1.5 work per h.

His partner makes 1/4.5 work per h.

Together they make (1/1.5 + 1/4.5) = (3/4.5 + 1/4.5) = 4/4.5 work per h.

They will work

1 : 4/4.5 = 4.5/4 = 1.125 h = 1 h + 0.125 h = 1h + 0.125h*60min/1h =

=1h 7.5 min = 1 h 7 min 30 sec