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Finding the Fourth Proportional to 261.20, 391.86 and 78.60

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Solution

The fourth proportional to 261.20, 391.86 and 78.60 is: 117.92

Step by Step Solution

  1. Step 1: Write the proportion equation
    261.20 : 391.86 = 78.60 : x
  2. Step 2: Convert to fraction form
    261.20/391.86 = 78.60/x
  3. Step 3: Cross multiply
    261.20x = 391.86 × 78.60
  4. Step 4: Simplify right side
    261.20x = 30,800.20
  5. Step 5: Solve for x
    x = 30,800.20/261.20
  6. Step 6: Final answer
    x = 117.92

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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.