Homework Help: Math

Posted by Meghan on Wednesday, March 24, 2010 at 12:31pm.

One grocery clerk can stock a shelf in 40 min, whereas a second clerk requires 20 min to stock the same shelf. How long would it take to stock the shelf if the two clerks worked together?
Is this how you do this:

t/40 + t/24 =1
t*3/40*3 + t*5/24*5 =1
3t/120 + 5t/120 =1
(8t/120)*120 = 1(120)
8t/8 = 120/8
=15

Math - Reiny, Wednesday, March 24, 2010 at 4:41pm
No,

rate of first = 1/40
rate of second = 1/20
combined rate = 1/40 + 1/20 = 3/40

so time for job = 1/(3/40) = 40/3 minutes
or 13 1/3 minutes

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