Percent Change, Percent Error, Simple Interest

Test Review - Percent of Change, Percent Error, Simple Interest

Use the information on the next few slides to help make your cheat sheet. Consider writing formulas, definitions, and procedures.

Percent change describes the change over time by either an increase or decrease.

Change is the difference between the new and original values.

Look for words and phrases like percentage increase/decrease, reduced by, increased by, percent of change.

Increases are positive (+)
Decreases are negative (-)

Percent of Change

Percent error compares the difference between an approximate value and an exact value to the exact value.

Other words for approximate: guess, estimate, about, near, close to, expected

Other words for exact: actual, is, was

Percent error problems are straight forward. They will usually ask to find the percent error.

Percent Error

Identify the I, p, r, and t from the problem. Substitute the known values in the formula and solve.

Remember, the interest rate needs to be written as a decimal and the time should be in years.

Example: 3% = 0.03; 2.5% = 0.025
Example: 36 months = 3 years; 18 months = 1.5 years

Total Value is the interest earned + the principal

Simple interest is interest earned on the principal, or original amount deposited in the account.

Find simple interest by using the Simple Interest formula:
I = p⋅r⋅t

I = Interest Earned
p = principal (original or initial deposit, investment)
r = Interest Rate (expressed as a decimal)
t = time (in years)

Simple Interest

​Finding Principal (p)

More Simple Interest Formulas

​Finding Rate (r)

​Finding Time (t)

Fractions, Decimals, Percents

​Conversions

Percent to a decimal: divide by 100 or move decimal 2 places to the left.
Decimal to a percent: multiply by 100 or move decimal 2 places to the right.
Fraction to a decimal: numerator divided by the denominator.

Multiple Choice

What type of problem?

Ann works in the grocery store and makes $12 per hour. If her pay is increased to $15 per hour, what is the percent increase in her pay?

• Percent of Change

• Percent Error

• Simple Interest

Multiple Choice

What type of problem?

A hospital bill is estimated to be $480. The actual bill ends up costing the patient $524.04. What is the percent error in the bill?

• Percent of Change

• Percent Error

• Simple Interest

Multiple Choice

What type of problem?

At the beginning of the school year, Anderson Middle School had 480 students. At the end of the school year, it had 504 students. What is the percent increase in enrollment?

• Percent of Change

• Percent Error

• Simple Interest

Multiple Choice

What type of problem?

Marco calculated he could run a 5K race in 28 minutes. He actually ran the race in 26 minutes. What is the percent error in his estimation?

• Percent of Change

• Percent Error

• Simple Interest

Multiple Choice

What type of problem?

Amanda invests $5,000 in a CD at an annual interest rate of 2.7%. How much interest will she earn at the end of 3 years?

• Percent of Change

• Percent Error

• Simple Interest

Multiple Choice

What type of problem?

Janice borrows $2,000 to purchase new living room furniture. She will pay an 18% interest rate over 18 months. How much will Janice pay in interest?

• Percent of Change

• Percent Error

• Simple Interest

Multiple Choice

What type of problem?

The weekly sales of a magazine increased from 500,000 to 600,000. By what percentage did the magazine sales increase?

• Percent of Change

• Percent Error

• Simple Interest

Multiple Choice

What is 2.75% as a decimal?

• 2.75

• 0.0275

• 0.275

• 27.5

Multiple Choice

6 months is how many years?

• 0.6 years

• 6 years

• 1.5 years

• 0.5 years

Multiple Choice

Convert 0.125 to a percent.

• 0.125%

• 1.25%

• 12.5%

• 125%

Multiple Choice

Convert 36 months to years.

• 3.6 years

• 3 years

• 4 years

• 0.36 years

Multiple Choice

What is 1.03 as a percent?

• 1.03%

• 103%

• 10.3%

• 0.0103%

Multiple Choice

What is 16% as a decimal?

• 0.16

• 16.0

• 1.6

• 0.016

Multiple Choice

A box of snacks contained 20 individual packages. The newly designed box contains 28 individual packages. By what percent did the number of individual packages increase?

• 40%

• 140%

• 28.5%

• 71%

Multiple Choice

At the beginning of the school year, Anderson Middle school had 480 students. At the end of the school year, it had 504 students. By what percentage did the student enrollment increase?

• 5%

• 105%

• 4.76%

• 11.5%

Multiple Choice

Airfare from Atlanta, GA to Nashville, TN changed from $250 per ticket to $180 per ticket. By what percentage did the cost of the airfare change?

• An increase of 28%

• A decrease of 28%

• An increase of 39%

• A decrease of 39%

Multiple Choice

Students are asked to estimate the number of gumballs in a jar. Ian guessed there are 228 gumballs in the jar. In actuality, there are 240 gumballs. What is the percent error?

• 3.5%

• 6%

• 5%

• 12%

Multiple Choice

Marco estimated he could run a 5K race in 28 minutes. He actually ran the race in 26 minutes. What is the percent error in his estimation?

• 15%
• 7.7%

• 10.8%

• 5%

Multiple Choice

Mrs. Baxter deposits $2,000 in an account that earns 5% simple interest. How much is her total investment worth after 8 years?

• $2800

• $2012.50

• $800

• $10,000

Multiple Choice

Little Johnny deposited $100 into a savings account. After 16 years, he earned $64 in interest. Find the interest rate of his savings account.

• 4%

• 0.4%

• 10.24%

• 25%

Multiple Choice

Harmon wants to earn $800 in interest so he'll have enough money to buy a used car. He puts $8000 into an account with an interest rate of 8%. How long will he need to leave the money in the account to earn $800 in interest?

• 1 year

• 1.25 years

• 2 years

• 2.5 years

Multiple Choice

Coach Jones made a deposit into an account that earns 2.5% interest. After 36 months, Coach Jones earned $135. How much was his initial deposit?

• $1800

• $1012.50

• $121.50

• $180