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Finding the Fourth Proportional to 139.71, 209.40 and 78.90

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Solution

The fourth proportional to 139.71, 209.40 and 78.90 is: 118.26

Step by Step Solution

  1. Step 1: Write the proportion equation
    139.71 : 209.40 = 78.90 : x
  2. Step 2: Convert to fraction form
    139.71/209.40 = 78.90/x
  3. Step 3: Cross multiply
    139.71x = 209.40 × 78.90
  4. Step 4: Simplify right side
    139.71x = 16,521.66
  5. Step 5: Solve for x
    x = 16,521.66/139.71
  6. Step 6: Final answer
    x = 118.26

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Why These Related Problems?

These problems maintain the same ratio (1.50) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.