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 xx represent the unknown number:
  1. "Five less than twice a number."
  2. "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 8787. 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 33 times as old as his son. In 1212 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 7070. 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 (0%0\% salt) must be added to 1010 liters of a 15%15\% salt solution to dilute it to a 10%10\% salt solution?

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Example

Example 2: Combining Two Active Solutions (Intermediate) A chemist needs to create 5050 mL of a 30%30\% acid solution by mixing a 20%20\% acid solution and a 45%45\% 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: Rate×Time=Work Done\text{Rate} \times \text{Time} = \text{Work Done}. To combine workers, add their individual rates.

Example

Example 1: Working Together (Basic) Pump A can fill a tank in 44 hours. Pump B can fill the same tank in 66 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 88 hours. However, a leak at the bottom can empty the full reservoir in 1212 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: D=R×TD = R \times T (Distance = Rate ×\times 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 6060 mph. Two hours later, Train B leaves the same station on a parallel track, traveling in the same direction at 9090 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 4040 mph, and returns along the same route at 6060 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 tt and units digit uu has a value of 10t+u10t + u.

Example

Example 1: Sum of Digits and Reversing (Advanced) The sum of the digits of a two-digit number is 1212. If the digits are reversed, the new number is 1818 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 I=PrtI = Prt.

Example

Example 1: Two Investments (Intermediate) A total of \10,000isinvestedintwoaccounts.Oneaccountpaysis invested in two accounts. One account pays5%annualinterest,andtheotherpaysannual interest, and the other pays8%annualinterest.Ifthetotalinterestearnedafteroneyearisannual interest. If the total interest earned after one year is$680$, 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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