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Finding the Fourth Proportional to 78.40, 108 and 61.12

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Solution

The fourth proportional to 78.40, 108 and 61.12 is: 84.20

Step by Step Solution

  1. Step 1: Write the proportion equation
    78.40 : 108 = 61.12 : x
  2. Step 2: Convert to fraction form
    78.40/108 = 61.12/x
  3. Step 3: Cross multiply
    78.40x = 108 × 61.12
  4. Step 4: Simplify right side
    78.40x = 6,600.96
  5. Step 5: Solve for x
    x = 6,600.96/78.40
  6. Step 6: Final answer
    x = 84.20

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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.