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Lesson 5-8. Simple Interest. Definition. Interest - the amount of money paid or earned for the use of money FORMULA FOR INTEREST - I = p r t I = interest P - principal (money invested or borrowed) R - rate - annual interest rate as a decimal. T - Time written in years.
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Lesson 5-8 Simple Interest
Definition • Interest- the amount of money paid or earned for the use of money • FORMULA FOR INTEREST - I = p r t • I = interest • P - principal (money invested or borrowed) • R - rate - annual interest rate as a decimal. • T - Time written in years
Example 1Find Simple Interest Find the simple interest for $500 invested at 6.25% for 3 years. I = prt I = 500 0.0625 3 I = $93.75
Practice ProblemFind Simple Interest Find the simple interest for $2000 invested at 5.5% for 4 years. I = prt I = 2000 0.055 4 I = $440
Example 2Find The Total Amount Find the total amount of money in an account where $95 is invested at 7.5% for 8 months. I = prt I = 95 0.075 ⅔ I = $4.75 Total = 95 + 4.75 = $99.75
Practice ProblemFind The Total Amount Find the total amount in an account where $250 is invested at 6% for 6 months. I = prt I = 250 0.06 ½ I = $7.5 Total = 250 + 7.50 = $257.50
Example 3Find The Interest Rate Tonya borrowed $3,600 to buy a used car. She will be paying $131.50 each month for the next 36 months. Find the simple interest rate for her loan. Find the total Tonya will pay. $131.50 36 = $4734 Find the interest. $4734 – $3600 = $1134 I = prt 1134 = 3600 r 3 (years) 0.105 = r Multiply by 100 to turn it into a percentage r = 10.5%
Practice ProblemFind The Interest Rate Gerardo borrowed $4,500 from his bank for home improvements. He will repay the loan by paying $120 a month for the next four years. Find the simple interest rate of the loan. Find the total Gerardo will pay. $120 48 = $5760 Find the interest. $5760 – $4500 = $1260 I = prt 1260 = 4500 r 4 0.07 = r Multiply by 100 to turn it into a percentage r = 7%