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Finding the Fourth Proportional to 76.80, 115.20 and 19.80

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Solution

The fourth proportional to 76.80, 115.20 and 19.80 is: 29.70

Step by Step Solution

  1. Step 1: Write the proportion equation
    76.80 : 115.20 = 19.80 : x
  2. Step 2: Convert to fraction form
    76.80/115.20 = 19.80/x
  3. Step 3: Cross multiply
    76.80x = 115.20 × 19.80
  4. Step 4: Simplify right side
    76.80x = 2,280.51
  5. Step 5: Solve for x
    x = 2,280.51/76.80
  6. Step 6: Final answer
    x = 29.70

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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.