Pre-Calculus: 1001 Practice Problems For Dummies (+ Free Online Practice). Mary Jane Sterling

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Applying Logarithms to Everyday Life

       381–390 Use the given formula and properties of logarithms to answer the question.

      381. Orange juice has a hydrogen ion concentration of 0.001 moles/liter. What is the pH of orange juice? Use the pH formula , where H+ is the hydrogen ion concentration in moles/liter.

      382. Ammonia water has a pH of 11.6. What is its hydrogen ion concentration (in moles/liter)? Use the pH formula , where H+ is the hydrogen ion concentration in moles/liter.

      383. You invest $5,000 in an account at an annual rate of 1.475% with interest compounding quarterly. Find out how much is in the account (to the nearest cent) after 3 years by using the compound interest formula , where A is the total amount in the account in dollars, P is the principal (amount invested), r is the annual interest rate, n is the number of times compounded per year, and t is the time in years.

384. If you invest $1,000 at a rate of 3.25%, compounded continuously, how many years would it take for your money to double? Round to the nearest hundredth of a year. Use the continuous compound interest formula , where A is the amount in the account, P is the principal, r is the interest rate, and t is the time in years.

      385. You buy a car that costs $23,495, and it loses $4,500 in value when you drive it off the car lot. The car then loses 10.785% in value each year (exponential depreciation). Rounded to the nearest cent, what is the value of the car after 5 years? Use the exponential equation , where y is the resulting value, C is the initial amount, k is the growth or decay rate, and t is the time in years.

      386. A normal conversation is 60 decibels (dB). What is the intensity of the sound of the conversation (in watts per square meter)? Use the following formula, where L is decibels and I is the intensity of the sound: .

      387. Two earthquakes

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