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Finding the Fourth Proportional to 211.89, 317.70 and 81.90

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Solution

The fourth proportional to 211.89, 317.70 and 81.90 is: 122.79

Step by Step Solution

  1. Step 1: Write the proportion equation
    211.89 : 317.70 = 81.90 : x
  2. Step 2: Convert to fraction form
    211.89/317.70 = 81.90/x
  3. Step 3: Cross multiply
    211.89x = 317.70 × 81.90
  4. Step 4: Simplify right side
    211.89x = 26,018.74
  5. Step 5: Solve for x
    x = 26,018.74/211.89
  6. Step 6: Final answer
    x = 122.79

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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.