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Finding the Fourth Proportional to 86.21, 128.34 and 85.70

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Solution

The fourth proportional to 86.21, 128.34 and 85.70 is: 127.58

Step by Step Solution

  1. Step 1: Write the proportion equation
    86.21 : 128.34 = 85.70 : x
  2. Step 2: Convert to fraction form
    86.21/128.34 = 85.70/x
  3. Step 3: Cross multiply
    86.21x = 128.34 × 85.70
  4. Step 4: Simplify right side
    86.21x = 10,998.74
  5. Step 5: Solve for x
    x = 10,998.74/86.21
  6. Step 6: Final answer
    x = 127.58

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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.