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Finding the Fourth Proportional to 85.42, 128.08 and 31.28

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Solution

The fourth proportional to 85.42, 128.08 and 31.28 is: 46.90

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.42 : 128.08 = 31.28 : x
  2. Step 2: Convert to fraction form
    85.42/128.08 = 31.28/x
  3. Step 3: Cross multiply
    85.42x = 128.08 × 31.28
  4. Step 4: Simplify right side
    85.42x = 4,006.34
  5. Step 5: Solve for x
    x = 4,006.34/85.42
  6. Step 6: Final answer
    x = 46.90

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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.