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Grade 9 · Math · Algebra 1

9th grade Compound interest with a formula worksheet

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Compound interest with a formula

Grade 9 Math Worksheet

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Circle the best answer, or write your answer on the line.

  1. Ms. Frost puts $1,000 in a pretend account at 6% a year, compounded monthly, for 3 years. Milo uses A = P(1 + r/n)^(nt). To the nearest cent, what is the balance?

  2. Ms. Hale puts $600 in a pretend account at 3% a year, compounded twice a year, for 5 years. Pia uses A = P(1 + r/n)^(nt). To the nearest cent, what is the balance?

  3. Mr. Cole puts $400 in a pretend account at 5% a year, compounded monthly, for 1 year. Ren uses A = P(1 + r/n)^(nt). To the nearest cent, what is the balance?

  4. Ms. Shaw puts $5,000 in a pretend account at 2% a year, compounded quarterly, for 4 years. Tala uses A = P(1 + r/n)^(nt). To the nearest cent, what is the balance?

  5. The class pretend fund holds $800 at 4% a year, compounded monthly, for 3 years. Zee wants only the interest. To the nearest cent, how much interest is earned?

  6. Mr. Grove's pretend account holds $1,500 at 6% a year, compounded quarterly, for 2 years. Ari wants only the interest. To the nearest cent, how much interest is earned?

  7. Ms. Wells's pretend account holds $300 at 5% a year, compounded twice a year, for 4 years. Bo wants only the interest. To the nearest cent, how much interest is earned?

  8. Mr. Cole puts $750 in a pretend account at 3% a year, compounded monthly, for 4 years. Jun checks the formula. Which one gives the balance?

    • A = 750(1 + 0.03)^(12 · 4)
    • A = 750(1 + 0.03/12)^4
    • A = 750(1 + 0.03/12)^(12 · 4)
    • A = 750(1 + 3/12)^(12 · 4)
  9. The class puts $500 in a pretend account at 6% a year, compounded twice a year, for 3 years. Luz checks the formula. Which one gives the balance?

    • A = 500(1 + 6/2)^(2 · 3)
    • A = 500(1 + 0.06/2)^(2 · 3)
    • A = 500(1 + 0.06/2)^3
    • A = 500(1 + 0.06)^(2 · 3)
  10. Mr. Vance puts $2,000 in a pretend account at 5% a year, compounded monthly, for 2 years. Milo checks the formula. Which one gives the balance?

    • A = 2000(1 + 0.05)^(12 · 2)
    • A = 2000(1 + 0.05/12)^(12 · 2)
    • A = 2000(1 + 5/12)^(12 · 2)
    • A = 2000(1 + 0.05/12)^2
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9th grade Compound interest with a formula worksheet – printable
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About this worksheet

Compound interest with a formula. Every version has 10 questions, and the answer key prints on the second page.

What your child will learn

  • I can find r/n and nt for an account and use A = P(1 + r/n)^(nt).
  • I can tell the balance from the interest, and find either one to the nearest cent.
  • I can compare compounding monthly, quarterly and yearly, and work back to the deposit.

Standard: A-SSE.A.1b, F-LE.A.1c

Words to know

compound interest: Interest that also earns interest, because it is added to the balance.

compounded quarterly / monthly: Interest is added 4 times a year / 12 times a year.

P, r, n, t: Deposit, yearly rate as a decimal, times per year, number of years.

r/n: The rate for one period: the yearly rate shared among the periods.

nt: The number of periods: times per year × years.

balance: Everything in the account: the deposit plus the interest.

Common mistakes

Your child used the whole yearly rate for each period instead of sharing it among the periods.

Your child used the percent as a whole number (6 instead of 0.06) in the formula.

Your child multiplied the yearly rate by the number of periods instead of dividing.

What to say

Ask: if interest is added 12 times a year, what part of the yearly rate is added each time?

Ask: what is 6% as a decimal?

Ask: should each period get more or less than the whole yearly rate?

Questions parents ask

What is the most common mistake with compound interest with a formula?

Your child used the whole yearly rate for each period instead of sharing it among the periods.

How can I help my child with compound interest with a formula?

Ask: if interest is added 12 times a year, what part of the yearly rate is added each time?

Are these 9th grade math worksheets free to print?

Yes. All 6 printable versions at each level are free to print, with the answer key, and no account is needed.

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