202 Chapter 2 Linear Equations and Inequalities Section 2.5 Applications Involving Percents Key Concepts The following formula will help you solve basic percent problems. Amount (percent)(base) One common use of percents is in computing sales tax. Another use of percent is in computing simple interest using the formula: interestb 1principal2°annual aSimple or I = Prt. interest rate ¢atime in years b Examples Example 1 A flat screen television costs $1260.00 after a 5% sales tax is included.What was the price before tax? a Price 1tax2 total ab pricex 0.05x 1260 1.05x 1260 The television cost $1200 before tax. Example 2 John Li invests $5400 at 2.5% simple interest. How much interest does he earn after 5 years? I Prt I 1$5400210.0252152 I $675 x 1200 before taxb Section 2.6 Literal Equations and Applications of Geometry Key Concepts A literal equation is an equation that has more than one variable. Often such an equation can be manipulated to solve for different variables. Formulas from Section R.4 can be used in applications involving geometry. Examples Example 1 P 2a b, solve for a. P b 2a b b P b 2a P b 2 P b 2 2a 2 a or a P b 2 Example 2 Find the length of a side of a square whose perimeter is 28 ft. P 4s Use the formula . Substitute 28 for P and solve: P 4s 28 4s 7 s The length of a side of the square is 7 ft.
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