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Finding the Fourth Proportional to 86.45, 128.90 and 85.39

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Solution

The fourth proportional to 86.45, 128.90 and 85.39 is: 127.32

Step by Step Solution

  1. Step 1: Write the proportion equation
    86.45 : 128.90 = 85.39 : x
  2. Step 2: Convert to fraction form
    86.45/128.90 = 85.39/x
  3. Step 3: Cross multiply
    86.45x = 128.90 × 85.39
  4. Step 4: Simplify right side
    86.45x = 11,006.13
  5. Step 5: Solve for x
    x = 11,006.13/86.45
  6. Step 6: Final answer
    x = 127.32

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Why These Related Problems?

These problems maintain the same ratio (1.49) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.