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Finding the Fourth Proportional to 85.79, 128.55 and 81.18

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Solution

The fourth proportional to 85.79, 128.55 and 81.18 is: 121.65

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.79 : 128.55 = 81.18 : x
  2. Step 2: Convert to fraction form
    85.79/128.55 = 81.18/x
  3. Step 3: Cross multiply
    85.79x = 128.55 × 81.18
  4. Step 4: Simplify right side
    85.79x = 10,436.48
  5. Step 5: Solve for x
    x = 10,436.48/85.79
  6. Step 6: Final answer
    x = 121.65

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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.