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Finding the Fourth Proportional to 86, 128.40 and 76.88

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Solution

The fourth proportional to 86, 128.40 and 76.88 is: 114.78

Step by Step Solution

  1. Step 1: Write the proportion equation
    86 : 128.40 = 76.88 : x
  2. Step 2: Convert to fraction form
    86/128.40 = 76.88/x
  3. Step 3: Cross multiply
    86x = 128.40 × 76.88
  4. Step 4: Simplify right side
    86x = 9,871.39
  5. Step 5: Solve for x
    x = 9,871.39/86
  6. Step 6: Final answer
    x = 114.78

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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.