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Finding the Fourth Proportional to 90, 133.92 and 86.40

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Solution

The fourth proportional to 90, 133.92 and 86.40 is: 128.56

Step by Step Solution

  1. Step 1: Write the proportion equation
    90 : 133.92 = 86.40 : x
  2. Step 2: Convert to fraction form
    90/133.92 = 86.40/x
  3. Step 3: Cross multiply
    90x = 133.92 × 86.40
  4. Step 4: Simplify right side
    90x = 11,570.69
  5. Step 5: Solve for x
    x = 11,570.69/90
  6. Step 6: Final answer
    x = 128.56

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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.