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Finding the Fourth Proportional to 85.75, 128.68 and 78.80

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Solution

The fourth proportional to 85.75, 128.68 and 78.80 is: 118.24

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.75 : 128.68 = 78.80 : x
  2. Step 2: Convert to fraction form
    85.75/128.68 = 78.80/x
  3. Step 3: Cross multiply
    85.75x = 128.68 × 78.80
  4. Step 4: Simplify right side
    85.75x = 10,139.14
  5. Step 5: Solve for x
    x = 10,139.14/85.75
  6. Step 6: Final answer
    x = 118.24

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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.