TITLE: Calculating Trump's Approval Rating for Non-Republicans
QUESTION [6 upvotes]: My father asked me this question yesterday, and as a math major I was a little embarrassed that I was not immediately sure that the answer I obtained was correct.
He asked:

If President Trump's overall approval rating is 38% among 125 million total voters, and the approval rating among the 56 million republican voters is 80%, then what is the approval rating of the other 69 million non-republican voters?

Is this a weighted averages sort of problem?
I set up my equation as:
$$0.448\times 0.8 + 0.552 \times x = 0.38$$
Thus $$x= 0.039$$
giving an approval rating of 3.9%.  
Is this correct?

REPLY [6 votes]: Yes, this is correct.
Maybe this will be more clear:
Total number of approvals: $0.38 \times 125 = 47.5$
Number of approvals among republicans: $0.8 \times 56 = 44.8$
Number of approvals among non-republicans: $x \times 69$
$47.5 = 44.8 + x \times 69$
$x = 0.039$