Oops! Thanks to Judy’s sharp eye, she caught a mistake I made in this video! After I calculated the interest to be $16 I only added $6 to the $800. The balance should be $816 instead of 806 after the first 6 months. That error affects my next calculations as well. For sure you’ll catch it when you go to score, but that’s the reason that number is wrong.
One more thing . . . . Judy suggested that that instead of multiplying by 0.25 or 0.5 for quarterly or semi-annual interest, you might find it easier to divide by 4 for quarterly, and divide by 2 for semi-annual. In the problem 15, the interest for the first year was $32, but we could divide by 2 since there are two semi-annual periods in a year, and get the $16 answer for interest earned. Hope that helps!