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Finding the Fourth Proportional to 78.21, 107.82 and 65.91

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Solution

The fourth proportional to 78.21, 107.82 and 65.91 is: 90.86

Step by Step Solution

  1. Step 1: Write the proportion equation
    78.21 : 107.82 = 65.91 : x
  2. Step 2: Convert to fraction form
    78.21/107.82 = 65.91/x
  3. Step 3: Cross multiply
    78.21x = 107.82 × 65.91
  4. Step 4: Simplify right side
    78.21x = 7,106.42
  5. Step 5: Solve for x
    x = 7,106.42/78.21
  6. Step 6: Final answer
    x = 90.86

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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.