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Finding the Fourth Proportional to 208.78, 313.28 and 85.43

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Solution

The fourth proportional to 208.78, 313.28 and 85.43 is: 128.20

Step by Step Solution

  1. Step 1: Write the proportion equation
    208.78 : 313.28 = 85.43 : x
  2. Step 2: Convert to fraction form
    208.78/313.28 = 85.43/x
  3. Step 3: Cross multiply
    208.78x = 313.28 × 85.43
  4. Step 4: Simplify right side
    208.78x = 26,764.51
  5. Step 5: Solve for x
    x = 26,764.51/208.78
  6. Step 6: Final answer
    x = 128.20

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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.