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Finding the Fourth Proportional to 820.80, 1,231.80 and 639.75

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Solution

The fourth proportional to 820.80, 1,231.80 and 639.75 is: 960.09

Step by Step Solution

  1. Step 1: Write the proportion equation
    820.80 : 1,231.80 = 639.75 : x
  2. Step 2: Convert to fraction form
    820.80/1,231.80 = 639.75/x
  3. Step 3: Cross multiply
    820.80x = 1,231.80 × 639.75
  4. Step 4: Simplify right side
    820.80x = 788,044.05
  5. Step 5: Solve for x
    x = 788,044.05/820.80
  6. Step 6: Final answer
    x = 960.09

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Why These Related Problems?

These problems maintain the same ratio (1.50) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.