Question

Stan and Hilda can mow the lawn in 20 minutes if they work together. If Hilda works twice as fast as Stan, how long would it take Stan to mow the lawn alone?

Answer 1

1 hour

Answer 2

stan speed = s lawns/min

Hilda speed = 2s lawns/min

(s + 2s) = total speed in lawns/min

so
(s + 2s) (20 min) = 1 lawn

60 s = 1
s = 1/60 lawns/min
or
60 min/lawn

Answer 3

Yes, an hour, 60 min