If you borrow $500 from a credit union at 12% annual interest and $250 from a bank at 18% annual interest, what is the effective annual interest rate (that is, what single rate of interest on $750 would result in th same total amount of interest)?
Annual interest for one year at the rate 12% for $500 is given by,
I = Principal amount x number of years x rate/100
= 500*1*12/100 = 60 ...
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