work rate - GMATPrep question - Need expert help

[voodoo_child]

Jennifer works 10 hours a day on Monday, Wed and Friday, 11 hours a day on Tue and Thu, and 8 hours a day on Sat. If she earns $600 each week day, and $300 on Sat, what are her average earnings per hour over this 6-day period?


A)$55
B)$50.681
C)$560
D)$50
E)$60

Here's what I did :

M,W and T => Amount = $1800 and Hours = 60 => hourly wage = 1800/60=$60
Tue, Thu => Amount = 1200, Hours = 22 => hourly wage = 1200/22 = $600/11
S=> Amount = 300, Hours = 8 => hourly wage = 300/8 = $150/4

Now, average hourly wage =

($60 + ($600/11) + $(150/4))/3 = $50.681 == B.


Any thoughts what's wrong with this? It's incorrect.

[eagleeye]

Hi voodoo_child:

You are making a mistake because rather than finding the overall average, you are finding averages for different parts and then averaging the number of averages. This is how you should do it (always).

Average = (Total earnings)/(total hours) = (600*5+300)/(10*3+11*2+8) = 3300/60 = 55.

Let me know if this helps