Question 346608
One does 1/40 of the job per minute.
The other does 1/60 per minute.
Together, they do 1/40 + 1/60 per minute = 3/120 + 2/120 = 1/24 job per minute
--> 24 minutes per job
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Use the shortcut, product over sum:
40*60/(40+60) = 24 minutes