141 Solving a Percent Equation with an Unknown Base Example 3 Section 2.5 Applications Involving Percents Andrea spends 20% of her monthly paycheck on rent each month. If her rent payment is $950, what is her monthly paycheck? Solution: Step 1: Read the problem. Let x represent the amount of Step 2: Label the variables. Andrea’s monthly paycheck. The problem can be rephrased as: $950 is 20% of what number? Step 3: Write a verbal model. 950 0.20 Step 4: Write a mathematical equation. Step 5: Solve the equation. Divide both sides by 0.20. x 950 0.20x 950 0.20 0.20x 0.20 Andrea’s monthly paycheck is $4750. Step 6: Interpret the results. Skill Practice 4. In order to pass an exam, a student must answer 70% of the questions correctly. If answering 42 questions correctly results in a 70% score, how many questions are on the test? 2. Applications Involving Simple Interest One important application of percents is in computing simple interest on a loan or on an investment. Simple interest is interest that is earned on principal (the original amount of money invested in an account). The following formula is used to compute simple interest: a annual b interest rate a Simple b interest This formula is often written symbolically as For example, to find the simple interest earned on $2000 invested at 7.5% interest for 3 years, we have I P r t Interest 1$2000210.0752132 $450 I Prt. a time in years aprincipal b invested b 4750 x Answer 4. There are 60 questions on the test.
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