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Finding the Fourth Proportional to 85.65, 128.48 and 72.78

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Solution

The fourth proportional to 85.65, 128.48 and 72.78 is: 109.18

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.65 : 128.48 = 72.78 : x
  2. Step 2: Convert to fraction form
    85.65/128.48 = 72.78/x
  3. Step 3: Cross multiply
    85.65x = 128.48 × 72.78
  4. Step 4: Simplify right side
    85.65x = 9,351.47
  5. Step 5: Solve for x
    x = 9,351.47/85.65
  6. Step 6: Final answer
    x = 109.18

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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.