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Finding the Fourth Proportional to 86.90, 120.09 and 78.66

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Solution

The fourth proportional to 86.90, 120.09 and 78.66 is: 108.70

Step by Step Solution

  1. Step 1: Write the proportion equation
    86.90 : 120.09 = 78.66 : x
  2. Step 2: Convert to fraction form
    86.90/120.09 = 78.66/x
  3. Step 3: Cross multiply
    86.90x = 120.09 × 78.66
  4. Step 4: Simplify right side
    86.90x = 9,446.28
  5. Step 5: Solve for x
    x = 9,446.28/86.90
  6. Step 6: Final answer
    x = 108.70

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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.