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Finding the Fourth Proportional to 86.40, 129.72 and 38.40

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Solution

The fourth proportional to 86.40, 129.72 and 38.40 is: 57.65

Step by Step Solution

  1. Step 1: Write the proportion equation
    86.40 : 129.72 = 38.40 : x
  2. Step 2: Convert to fraction form
    86.40/129.72 = 38.40/x
  3. Step 3: Cross multiply
    86.40x = 129.72 × 38.40
  4. Step 4: Simplify right side
    86.40x = 4,981.25
  5. Step 5: Solve for x
    x = 4,981.25/86.40
  6. Step 6: Final answer
    x = 57.65

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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.