Question 442694
Don't try to remember how to do it, or remember a formula.
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Mary does 1/40 of the drive per minute.
Bill does 1/65 per minute.
That makes sense, right? Then,
Together, they do 1/40 + 1/65 per minute
Add those
= (65 + 40)/2600 per minute = 105/2600 per minute
That means,
--> 2600/105 mins per driveway
= 520/21 minutes