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Finding the Fourth Proportional to 86.40, 128.96 and 81.60

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Solution

The fourth proportional to 86.40, 128.96 and 81.60 is: 121.80

Step by Step Solution

  1. Step 1: Write the proportion equation
    86.40 : 128.96 = 81.60 : x
  2. Step 2: Convert to fraction form
    86.40/128.96 = 81.60/x
  3. Step 3: Cross multiply
    86.40x = 128.96 × 81.60
  4. Step 4: Simplify right side
    86.40x = 10,523.14
  5. Step 5: Solve for x
    x = 10,523.14/86.40
  6. Step 6: Final answer
    x = 121.80

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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.