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Finding the Fourth Proportional to 85.51, 128.20 and 31.38

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Solution

The fourth proportional to 85.51, 128.20 and 31.38 is: 47.05

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.51 : 128.20 = 31.38 : x
  2. Step 2: Convert to fraction form
    85.51/128.20 = 31.38/x
  3. Step 3: Cross multiply
    85.51x = 128.20 × 31.38
  4. Step 4: Simplify right side
    85.51x = 4,022.92
  5. Step 5: Solve for x
    x = 4,022.92/85.51
  6. Step 6: Final answer
    x = 47.05

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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.