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Finding the Fourth Proportional to 261.12, 391.68 and 90

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Solution

The fourth proportional to 261.12, 391.68 and 90 is: 135

Step by Step Solution

  1. Step 1: Write the proportion equation
    261.12 : 391.68 = 90 : x
  2. Step 2: Convert to fraction form
    261.12/391.68 = 90/x
  3. Step 3: Cross multiply
    261.12x = 391.68 × 90
  4. Step 4: Simplify right side
    261.12x = 35,251.20
  5. Step 5: Solve for x
    x = 35,251.20/261.12
  6. Step 6: Final answer
    x = 135

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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.