Planning Ahead Saving money is an important part of financial freedom and responsibility. What are the advantages of having a savings account?
Mar 27, 2015
Planning Ahead
Saving money is an important part of financial freedom and responsibility.
What are the advantages of having a savings account?
compound interest table
A tool to calculate compound interest quickly.
compound interest table
A tool to calculate compound interest quickly.
Lesson Objective Find compound interest using a table and the compound interest formula.
Content Vocabulary
compound interest table
State Bank pays 6 percent interest compounded quarterly on regular savings accounts. You deposited $3,000 for 2 years. You made no deposits or withdrawals.
How much interest did you earn in 2 years?
(Note: Use the Compound table on page A11 of your textbook to solve this problem.)
Example 1Example 1
Find the total interest periods.
Periods per Year × Number of Years
4 quarters per year × 2 years = 8 periods
Example 1 Answer: Example 1 Answer: Step 1Step 1
Find the interest rate per period.
Periods per Year × Number of Years
Annual Rate ÷ Number of Periods per Year
6% ÷ 4 = 1.5%
Example 1 Answer: Example 1 Answer: Step 2Step 2
Find the amount for 8 periods at 1.5 percent per period using the Compound Interest—Amount of $1.00 table on page A11 of your textbook.
It is 1.12649.
Example 1 Answer: Example 1 Answer: Step 3Step 3
Find the amount.
Original Principal × Amount of $1.00
$3,000.00 × 1.12649 = $3,379.47
Example 1 Answer: Example 1 Answer: Step 4Step 4
Find the compound interest.
Amount – Original Principal
$3,379.47 – $3,000.00 = $379.47
Example 1 Answer: Example 1 Answer: Step 5Step 5
Juan Lopez opens an account and deposits $4,379.47. The account pays 6 percent annual interest and compounds quarterly. Six months later he deposits $2,000.
How much will he have in the account in 1½ more years if he continues to pay 6 percent interest compounded quarterly?
Example 2Example 2
Find the total interest periods for first 6 months.
Periods per Year × Number of Years
4 quarters per year × ½ year = 2 periods
Example 2 Answer: Example 2 Answer: Step 1Step 1
Find the interest rate per period.
Annual Rate ÷ Number of Periods per Year
6% ÷ 4 = 1.5%
Example 2 Answer: Example 2 Answer: Step 2Step 2
Find the amount of $1.00 for 2 periods at 1.5 percent per period using the Compound Interest—Amount of $1.00 table on page 797.
It is 1.03023.
Example 2 Answer: Example 2 Answer: Step 3Step 3
Find the amount for 6 months.
Original Principal × Amount of $1.00
$4,379.47 × 1.03023 = $4,511.86 (new principal)
Example 2 Answer: Example 2 Answer: Step 4Step 4
Find the amount for 1.5 years.
Periods per Year × Number of Years
4 quarters per year × 1.5 years = 6 periods
Example 2 Answer: Example 2 Answer: Step 5Step 5
Find the amount of $1.00 for 6 periods at 1.5 percent per paid using the Compound Interest—Amount of $1.00 table on page 797.
It is 1.09344.
Example 2 Answer: Example 2 Answer: Step 6Step 6
Find the amount for 1.5 years.
New Principal × Amount of $1.00
($4,511.86 + $2,000.00) × 1.09344 =
$6,511.86 × 1.09344 = $7,120.33
Example 2 Answer: Example 2 Answer: Step 7Step 7
$8,240 invested at 5.75 percent compounded semiannually for 3 years.
No additional deposits or withdrawals.
Find the amount.
Practice 1Practice 1
$8,240 x 1.18538 = $9,767.53
Practice 1 AnswerPractice 1 Answer
$1,900 invested at 6.25 percent compounded semiannually for 5 years.
No additional deposits or withdrawals.
Find the amount.
How much interest did the money earn in 5 years?
Practice 2Practice 2
$1,900 invested at 6.25 percent compounded semiannually for 5 years:
1,900 x 1.36032 = $2,584.61
Interest earned in 5 years:
2,584.61 – 1900 = 2,584.61 – 1900 = $684.61
Practice 2 AnswerPractice 2 Answer