If the interest rate on a savings account is 0.02%, approximately how much money do you need to keep in this account for 1 year to earn enough interest to cover a single $9.99 below-minimum-balance fee

So, we need to gain at least 9.99$ from the interest rate. Hence, if we store x, we will gain x*0.02% and thus x*0.02%>9.99 must hold. We need to convert the percentage to a decimal: 0.02%=0.02/100=0.0002. Then, we have that x>9.99/0.0002. Doing the calculation, we have that x>49950$. This value is the least value that covers our fee exactly.

This is true for sure