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Finding the Fourth Proportional to 91.20, 136.22 and 78.40

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Solution

The fourth proportional to 91.20, 136.22 and 78.40 is: 117.10

Step by Step Solution

  1. Step 1: Write the proportion equation
    91.20 : 136.22 = 78.40 : x
  2. Step 2: Convert to fraction form
    91.20/136.22 = 78.40/x
  3. Step 3: Cross multiply
    91.20x = 136.22 × 78.40
  4. Step 4: Simplify right side
    91.20x = 10,679.21
  5. Step 5: Solve for x
    x = 10,679.21/91.20
  6. Step 6: Final answer
    x = 117.10

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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.