A Formula of Interest

Name Date Class

Challenge

A Formula of Interest

When you put your money in a savings account, the bank may pay you simple interest. Let P represent the dollar amount of your deposit (the principal), let r represent the interest rate, and let t represent the number
of years. The amount of interest you earn, I, is given by the simple interest formula: I = Prt.

Note that banks typically use percents to describe their interest rates. Percent means “per hundred,” so an interest rate of 5% means that you should use r = or 0.05.

Use the simple interest formula to solve the following problems:

1. If P = 2500, r = 0.03, and t = 5, what is I?

2. If r = 0.025, t = 3, and I = 150, what is P ?

3. If P = 500, r = 0.06, and I = 150, what is t?

4. If P = 3000, t = 4, and I = 384, what is r?

5. Kevin is making a deposit of $1800 at his local bank. The bank pays
6.5% simple interest (r = 0.065). If Kevin leaves his deposit at the
bank for 3 years, how much interest will he earn?

6. Cecelia made a deposit of $600 at a bank paying 4% simple interest
(r = 0.04). How long should she leave her deposit at the bank in
order to earn $72 in interest?

7. Darryl opened an account at a bank which paid 5.5% simple interest
(r = 0.055). After 6 years, he had earned $726 in interest. What was
the amount of his original deposit?

8. Sophia deposited $150 at a savings and loan association paying
simple interest. If she earned $27 in interest after 6 years, what
was the interest rate?

9. Nathan made a deposit of $650 at a bank paying 3.8% simple interest
(r = 0.038). If he leaves his deposit at the bank for 10 years, how much
interest will he earn?

10. Susie made a deposit of $980 at a credit union paying 7% simple
interest (r = 0.07). How long should she leave her deposit at the
credit union in order to earn $343 in interest?

11. Guillermo deposited $1350 at a bank paying simple interest. If he
earned $109.35 in 3 years, what was the interest rate?

2-40 Holt McDougal Algebra 1

Name Date Class

2-40 Holt McDougal Algebra 1

Practice C

1. w = 2. vf = at + vi

3. f = 4. a = 12 - 5b

5. x = 6. h =

7. r = s(t - 9) 8. n =

9. a. a = 10. a. t =

b. 19 m/s2 b. 8 years

Review for Mastery

1. s = 2. b = 180 - a – c

3. K = 4. w =

5. 12 in.

6. add –x to both sides

7. multiply both sides by 2

8. add 3r to both sides

9. a = 10. z = 3(y - x)

11. m = pn - 3

Challenge

1. l = 375 2. P = 2000

3. t = 5 years

4. r = 0.032 or 3.2%

5. $351 6. 3 years

7. $2200 8. 0.03 or 3%

9. $247 10. 5 years

11. 0.027 or 2.7%

Problem Solving

1. r = 2. 9.1 m/s

3. 8.5 m/s 4. 0.4 m/s

5. B 6. F

7. D 8. J

Reading Strategies

1. Possible answer: 3x + 2y = 9

2. The equation contains only one
variable, n.

3. Yes, because it has two or more variables.

4. Divide both sides by r.

5. t =

6. a. h =
b. 3 cm

LESSON 2-6

Practice A

1. -3; 2; -2; 2

2. -7; 7; 4; 4; 4; 4; -11; 3

3. 6; -6; 6; -5; 7

4. {-8, 8} 5. {-14, 14}

6. {-9, 9} 7. {-17, 17}

8. {-11, 7} 9. {-1, 11}

10. {-5, 5} 11. {-7, 3}

12. {-11, 9}

13.

14. 22 miles per gallon; 26 miles per gallon

Practice B

1. {-12, 12}

3. {-10, 10}

4. {-9, 9}

5. {-8, 8}

6. {-13, 7}

7. {-1, 3}

8. {2, 8}

9. {-14, 10}

10. {-3, 3}

A18 Holt McDougal Algebra 1