54 - Simple Interest 

+Emmanuel Sarpong Hi Emmanuel, Thank you for your comment. It makes me happy to see that someone is taking the time and effort to critically analyze the problems. Your question concerns the last example in the video, beginning at about video time 23.50/26.40. You asked why I didn't add the 1 to the 0.67. Is this correct? The balance, how much you will have in your account at some time in the future is equal to the principal, the amount of money you start with plus how much money you get from your account's interest. That amount is equal to the principal times the rate of interest times the time accumulated. As an equation, b = p + prt but here there is a p in both of the terms on the right. So factoring the p out we arrive with the equation b = p(1 + rt) the formula I started the problem using. Perhaps it would have been better rather than just saying I was using this equation to solve for r, it would have been better to start with a more detailed explanation of how we got to that equation. This has to do with order of operations in reading an equation. Multiplications are done before addition. b = p(1 + rt) = p + prt since I must multiply each of the terms in the parentheses by p rather than first adding the 1 to the rt term. Plugging in the numbers - I'll use to indicate a comment, not a mathematical operation. $12000 = $11000 + $11000 times r