Interest Problems

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# Interest Problems - PowerPoint PPT Presentation

Interest Problems. Interest Formula. Principal • Rate • Time = Interest Principal – money invested % Rate – change to a decimal Time – years. Example. James invested \$500 in a 2% CD. If simple interest were used by the bank, how much interest would he have at the end of 4 years?.

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## PowerPoint Slideshow about 'Interest Problems' - warren

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### Interest Problems

Interest Formula
• Principal • Rate • Time = Interest
• Principal – money invested
• % Rate – change to a decimal
• Time – years
Example
• James invested \$500 in a 2% CD. If simple interest were used by the bank, how much interest would he have at the end of 4 years?
Example
• Mr. Hawkey invested \$30,000 in two accounts. He made a total of \$2,140 annual interest. How much did he invest in each account if one account pays 7% annual interest and the other pays 8.5% annual interest?
Investment
• What is the total amount invested?
• \$30,000
Investment
• x = \$27,333.33 (invested at 7%)
Example
• A merchant has 2 loans totaling \$25,000. The interest rates are 6% and 7.5%. If the annual interest charge on the 6% loan is \$520 more than the 7.5% loan, how much has he borrowed at each rate?
Example
• Susan wants to invest the \$23,000 she earned in a year. Her bank has a savings account which earns 2.5% annually as well as a CD which earns 5.5%. Susan wants to put some money in each account, and she wants to earn at least \$1,000 by the end of the year. How much should she put in each?
Example
• Mr. and Mrs. Bell received a \$40,000 inheritance, so they decide to invest it in two different accounts and use the earned interest to go on a vacation. They put \$30,000 in a 5% CD and \$10,000 in a 3% money market account. If they need \$3,000, how long will they need to leave the money in these accounts?

### Mixture Problems

Mixture Problems
• quantity • percentage (strength) = the PART described by the percentage in the units described by the quantity
Mixture Problems
• 45 lbs. of 80% iodine solution
• 45 • 0.80 = x
• 36 lbs. of iodine
Mixture Problems
• What is the strength of a hydrochloric acid solution if there are 34 kilograms of water and 6 kilograms of acid?
• 40 • x = 6
• 15% strength
Example
• A pharmacist needs to make a facial cream that is 0.5% medicine and the rest lanolin. He has 80 grams of a 1.5% mixture in his lab. How much lanolin should he add to the mixture to make the desired strength?
Example
• The same pharmacist gets another order for 240 grams of 0.5% facial cream. From earlier orders, he has some 0.2% cream and some 0.8% cream. How much of each should he add together to get 240 g at the desired strength?
Section 2.6
• pp. 67-69
Problem 1
• Prt = I
• (148)(.06)(1) = I
• \$8.88 = I
Problems 2-3
• Quantity • Strength
• = 50(.03)
• = 1.5 gallons
• 12  30 = Strength
• 0.4 = Strength
• 40% Strength
Problem 4
• 120 + 150 = x
• x = \$270

P • r • t = I

3000 .04 1 120

2500 .06 1 150

Problem 5

1.1 + 0.42 = x

x = 1.52 gallons

Problem 7
• 0.085x + 0.1(15250 – x) = 1411.75
• \$7550 at 8.5%
• \$7700 at 10%

P •r • t = I

x .085 1 .085x

15250-x .1 1 .1(15250-x)

Problem 9

0.02x + 0.11(3 – x) = 0.24

1 kg of 2% HCl solution

2 kg of 11% HCl solution

Problem 10
• 4000x + 8200(x+.015) = 1282
• \$4000 at 9.5%
• \$8200 at 11%

P •r • t = I

4000 x 1 4000x

8200 x+.015 1 8200(x+.015)

Problem 13
• .075(152000 – x) + .105x = 13350
• \$65,000 at 21%
• \$87,000 at 15%

P •r • t = I

152000-x .15 .5 .075(152000-x)

x .21 .5 .105x

Problem 14
• 102x + 180x = 70.50
• x = 0.25
• ¼ of a year or 3 months

P •r • t = I

1200 .085 x 102x

2000 .09 x 180x

Problem 15

2 + x = 0.08(100 + x)

x  6.5 mL of pure acetic acid

Problem 16

9 = 0.001(300 + x)

x = 8700 liters of water