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Finding the Fourth Proportional to 120.21, 165.78 and 78.72

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Solution

The fourth proportional to 120.21, 165.78 and 78.72 is: 108.56

Step by Step Solution

  1. Step 1: Write the proportion equation
    120.21 : 165.78 = 78.72 : x
  2. Step 2: Convert to fraction form
    120.21/165.78 = 78.72/x
  3. Step 3: Cross multiply
    120.21x = 165.78 × 78.72
  4. Step 4: Simplify right side
    120.21x = 13,050.20
  5. Step 5: Solve for x
    x = 13,050.20/120.21
  6. Step 6: Final answer
    x = 108.56

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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.