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Finding the Fourth Proportional to 86, 128.90 and 51.78

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Solution

The fourth proportional to 86, 128.90 and 51.78 is: 77.61

Step by Step Solution

  1. Step 1: Write the proportion equation
    86 : 128.90 = 51.78 : x
  2. Step 2: Convert to fraction form
    86/128.90 = 51.78/x
  3. Step 3: Cross multiply
    86x = 128.90 × 51.78
  4. Step 4: Simplify right side
    86x = 6,674.44
  5. Step 5: Solve for x
    x = 6,674.44/86
  6. Step 6: Final answer
    x = 77.61

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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.