I don't think anyone is working on a double major. Most of the folks are doing Psychology as a second degree. In addition to your first degree, you must have thiry new hours credit.
Since you already have 12 Psych hours, you would need 18 new hours in Psychology and 12 hours in other credits.If the requirements for business are still the same, you will need more upper level Arts and Science credits in Psych than Business.
The requirements have changed since I earned mine and you should always check with your advisor.

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Chartered Life Underwriter-American College 1985
Chartered Financial Consultant-American College 1986
BS Charter Oak State College 2005
BS Psychology-Summa Cum Laude-Excelsior College 2006
Chartered Advisor for Senior Living-American College 2006