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Finding the Fourth Proportional to 85.76, 128.02 and 78.20

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Solution

The fourth proportional to 85.76, 128.02 and 78.20 is: 116.73

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.76 : 128.02 = 78.20 : x
  2. Step 2: Convert to fraction form
    85.76/128.02 = 78.20/x
  3. Step 3: Cross multiply
    85.76x = 128.02 × 78.20
  4. Step 4: Simplify right side
    85.76x = 10,011.16
  5. Step 5: Solve for x
    x = 10,011.16/85.76
  6. Step 6: Final answer
    x = 116.73

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