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Finding the Fourth Proportional to 100.72, 138.90 and 91

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Solution

The fourth proportional to 100.72, 138.90 and 91 is: 125.50

Step by Step Solution

  1. Step 1: Write the proportion equation
    100.72 : 138.90 = 91 : x
  2. Step 2: Convert to fraction form
    100.72/138.90 = 91/x
  3. Step 3: Cross multiply
    100.72x = 138.90 × 91
  4. Step 4: Simplify right side
    100.72x = 12,639.90
  5. Step 5: Solve for x
    x = 12,639.90/100.72
  6. Step 6: Final answer
    x = 125.50

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Why These Related Problems?

These problems maintain the same ratio (1.38) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.