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Finding the Fourth Proportional to 139.80, 209.80 and 85.72

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Solution

The fourth proportional to 139.80, 209.80 and 85.72 is: 128.64

Step by Step Solution

  1. Step 1: Write the proportion equation
    139.80 : 209.80 = 85.72 : x
  2. Step 2: Convert to fraction form
    139.80/209.80 = 85.72/x
  3. Step 3: Cross multiply
    139.80x = 209.80 × 85.72
  4. Step 4: Simplify right side
    139.80x = 17,984.06
  5. Step 5: Solve for x
    x = 17,984.06/139.80
  6. Step 6: Final answer
    x = 128.64

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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.