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Finding the Fourth Proportional to 91.20, 137.72 and 90.40

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Solution

The fourth proportional to 91.20, 137.72 and 90.40 is: 136.51

Step by Step Solution

  1. Step 1: Write the proportion equation
    91.20 : 137.72 = 90.40 : x
  2. Step 2: Convert to fraction form
    91.20/137.72 = 90.40/x
  3. Step 3: Cross multiply
    91.20x = 137.72 × 90.40
  4. Step 4: Simplify right side
    91.20x = 12,449.89
  5. Step 5: Solve for x
    x = 12,449.89/91.20
  6. Step 6: Final answer
    x = 136.51

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Why These Related Problems?

These problems maintain the same ratio (1.51) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.