Calculating weighted averages and totaling them?

Question

I am trying to combine two different ratings, Google Reviews and Yelp reviews. If I have lets say -
2 Yelp Reviews - Averaging to 2 Stars
10 Google Reviews - Averaging to 4.5 Stars

How would I be able to find the total average correctly if I were to combine the two with the weight?

Answer 1

average = total/count

 

So average * count = total

 

Google:

   4.5 = total/10  ---> total = 4.5*10 = 45

 

Yelp:  total = 2 * 2 = 4

 

The grand total is 45+4 = 49

That is over a total of 12 reviews.

 

So the composite average is 49/12 = 4 and 1/12 = 4.083