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November 2nd, 2015, 10:42 AM  #1 
Newbie Joined: Nov 2015 From: Dorchester Posts: 1 Thanks: 0  Need help with this question please!
I have been given the question: the mean on 4 numbers is 10 , the mean of a different set of 8 numbers is 7. What is the mean of all 12 numbers? Somebody please help me with this I don't understand it, thank you. 
November 2nd, 2015, 11:10 AM  #2 
Global Moderator Joined: Nov 2006 From: UTC 5 Posts: 16,046 Thanks: 938 Math Focus: Number theory, computational mathematics, combinatorics, FOM, symbolic logic, TCS, algorithms 
You know that (a1 + a2 + a3 + a4)/4 = 10 and that (b1 + b2 + ... + b8)/8 = 7. You're asked to find (a1 + a2 + a3+ a4 + b1 + ... + b8)/12. You can find a1 + a2 + a3 + a4 from the first average and b1 + b2 + ... + b8 from the second, and use that to find the final sum.
