Word Problems - Examples & Applications
Translating real-world scenarios into algebraic equations is a fundamental skill. This section walks through the complete process of defining variables, setting up equations, and solving classic problem archetypes.
General Strategy
Translating a word problem into an algebraic equation is often the most challenging step. These case studies show how to approach translation methodically.
Example
Case Study 1: Translating Key Phrases (Basic)
Translate the following phrases into algebraic expressions, letting represent the unknown number:
- "Five less than twice a number."
- "The sum of a number and seven, divided by three."
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Example
Case Study 2: Consecutive Integer Problem (Intermediate)
The sum of three consecutive odd integers is . Find the integers.
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1. Age Problems
Age problems require setting up variables for current ages and translating time-shifted relationships (past or future) into equations.
Example
Example 1: Basic Age Problem
A father is currently times as old as his son. In years, the father will be twice as old as his son. Find their current ages.
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Example
Example 2: Past and Future Constraints (Intermediate)
Ten years ago, Alice was twice as old as Bob. Five years from now, the sum of their ages will be . How old is Bob now?
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2. Mixture Problems
Mixture problems involve combining substances with different concentrations to achieve a desired final concentration or total amount. The key is to balance the total quantity and the active ingredient.
Example
Example 1: Diluting a Solution (Basic)
How many liters of pure water ( salt) must be added to liters of a salt solution to dilute it to a salt solution?
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Example
Example 2: Combining Two Active Solutions (Intermediate)
A chemist needs to create mL of a acid solution by mixing a acid solution and a acid solution. How much of each should she use?
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3. Work Problems
Work problems involve individuals or machines completing a task at different rates. The fundamental formula is: . To combine workers, add their individual rates.
Example
Example 1: Working Together (Basic)
Pump A can fill a tank in hours. Pump B can fill the same tank in hours. If both pumps work together, how long will it take to fill the tank?
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Example
Example 2: Working Against Each Other (Intermediate)
A pipe can fill a reservoir in hours. However, a leak at the bottom can empty the full reservoir in hours. If the pipe is turned on while the leak is active, how long will it take to fill the reservoir?
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4. Motion Problems (Distance-Rate-Time)
Motion problems rely on the formula: (Distance = Rate Time). Creating a table is highly recommended to organize the data for different moving objects or segments of a trip.
Example
Example 1: Catch-Up Problem (Basic)
Train A leaves a station traveling at mph. Two hours later, Train B leaves the same station on a parallel track, traveling in the same direction at mph. How long will it take Train B to catch up to Train A?
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Example
Example 2: Round Trip Average Speed (Advanced)
A driver travels from City X to City Y at an average speed of mph, and returns along the same route at mph. What is the driver's average speed for the entire round trip?
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5. Digit Problems
Digit problems involve numbers where the digits are represented by variables. A two-digit number with tens digit and units digit has a value of .
Example
Example 1: Sum of Digits and Reversing (Advanced)
The sum of the digits of a two-digit number is . If the digits are reversed, the new number is greater than the original number. Find the original number.
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6. Investment and Interest Problems
Investment problems often involve dividing a principal amount into two accounts with different interest rates. The formula used is .
Example
Example 1: Two Investments (Intermediate)
A total of \10,0005%8%$680$, how much was invested at each rate?
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7. Clock Problems
Clock problems often ask for the exact time the hands of an analog clock overlap or form a specific angle. The key is to use the relative speed between the minute hand and the hour hand.
Example
Example 1: Hand Overlap (Advanced)
At what exact time between 4:00 and 5:00 do the minute and hour hands of a clock overlap?
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