Suppose you deposit $80 into a savings account that earns an annual interest rate of six percent. How much interest would you earn in nine months?

1. $36
2. $4.80
3. $3.60
4. $0.40

You may have forgotten to convert the percent interest into a decimal. Here's how to get the correct answer:

To solve this problem, you need to use the formula I=Prt, in which the I is interest, the P is principle, the r is rate and the t is time. Thus, interest is equal to 80 times 0.06 (that's six percent as a decimal) times nine divided by 12. You need to divide nine by 12 because you left the money in the bank for nine months, which is only a part of the whole year that you are earning six percent interest for. So, 80 x 0.06 x 0.75 = 3.6. If you write that as an amount of money, it's $3.60.

You may have forgotten to place the time at nine out of 12 months. Here's how to get the correct answer:

To solve this problem, you need to use the formula I=Prt, in which the I is interest, the P is principle, the r is rate and the t is time. Thus, interest is equal to 80 times 0.06 (that's six percent as a decimal) times nine divided by 12. You need to divide nine by 12 because you left the money in the bank for nine months, which is only a part of the whole year that you are earning six percent interest for. So, 80 x 0.06 x 0.75 = 3.6. If you write that as an amount of money, it's $3.60.

You're correct! Check your work below:

To solve this problem, you need to use the formula I=Prt, in which the I is interest, the P is principle, the r is rate and the t is time. Thus, interest is equal to 80 times 0.06 (that's six percent as a decimal) times nine divided by 12. You need to divide nine by 12 because you left the money in the bank for nine months, which is only a part of the whole year that you are earning six percent interest for. So, 80 x 0.06 x 0.75 = 3.6. If you write that as an amount of money, it's $3.60.

That's incorrect. Here's how to get the correct answer:

To solve this problem, you need to use the formula I=Prt, in which the I is interest, the P is principle, the r is rate and the t is time. Thus, interest is equal to 80 times 0.06 (that's six percent as a decimal) times nine divided by 12. You need to divide nine by 12 because you left the money in the bank for nine months, which is only a part of the whole year that you are earning six percent interest for. So, 80 x 0.06 x 0.75 = 3.6. If you write that as an amount of money, it's $3.60.