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Finding the Fourth Proportional to 85.72, 128.52 and 31.60

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Solution

The fourth proportional to 85.72, 128.52 and 31.60 is: 47.38

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.72 : 128.52 = 31.60 : x
  2. Step 2: Convert to fraction form
    85.72/128.52 = 31.60/x
  3. Step 3: Cross multiply
    85.72x = 128.52 × 31.60
  4. Step 4: Simplify right side
    85.72x = 4,061.23
  5. Step 5: Solve for x
    x = 4,061.23/85.72
  6. Step 6: Final answer
    x = 47.38

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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.