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This section covers motion problems, distance problems, problems with two rates, money problems, and mixture problems. Learn how to solve various mathematical problems involving rates, time, distance, and money.
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Motion, Money and Mixture Problems Section 3.4
Motion Problems amount = rate · time A motion problemis one in which an object is moving at a specified rate for a specified period of time. Example: A typical shower uses 30 gallons of water and lasts for 6 minutes. How much water is typically used per minute? Continued.
Distance Problems When the amount in the formula is distance, we refer to the formula as the distance formula. distance = rate · time or d = r · t Example: While swimming in the ocean, Elyse’s glasses fell off her head. If the glasses fall at a rate of 4 feet per second, how long will it take for them to fall 70 feet to the sand at the bottom? Continued.
Problems with Two Rates Example: Two crews are laying blacktop on a road. They start at the same time at opposite ends of a 12-mile road and work toward one another. One crew lays blacktop at an average rate of 0.75 mile a day faster than the other crew. If the two crews meet after 3.2 days, find the rate of each crew. Continued.
Problems with Two Rates Example: Kelsey started driving to the mall at an average speed of 30 mile per hour. A short while later, she realized she forgot her wallet. She turned around and headed back to the house, driving 20 miles per hour. If it took her a total of 0.6 hours for the round trip, how far had she driven before she turned around? Continued.
Money Problems interest = principal · rate · time Example: Jordan invested $12,500, part at 7% simple interest and part at 6% simple interest for 1 year. How much was invested at each rate if each account earned the same interest? Continued.
Mixture Problems Any problem in which two or more quantities are combined to produce a different quantity may be considered a mixture problem. strength · quantity = amount
Mixture Problems Example: At a local pet store, bird food is sold in bulk. In one barrel are sunflower seeds that sell for $1.80 per pound. In another barrel is cracked corn that sells for $1.40 per pound. If the store makes bags of a mixture of the two by mixing 2.5 pounds of sunflower seeds with 1 pound of the cracked corn, what should be the cost per pound? Continued.