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Finding the Fourth Proportional to 86.80, 129.50 and 81.72

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Solution

The fourth proportional to 86.80, 129.50 and 81.72 is: 121.92

Step by Step Solution

  1. Step 1: Write the proportion equation
    86.80 : 129.50 = 81.72 : x
  2. Step 2: Convert to fraction form
    86.80/129.50 = 81.72/x
  3. Step 3: Cross multiply
    86.80x = 129.50 × 81.72
  4. Step 4: Simplify right side
    86.80x = 10,582.74
  5. Step 5: Solve for x
    x = 10,582.74/86.80
  6. Step 6: Final answer
    x = 121.92

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Why These Related Problems?

These problems maintain the same ratio (1.49) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.