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Finding the Fourth Proportional to 20.81, 31.21 and 8.78

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Solution

The fourth proportional to 20.81, 31.21 and 8.78 is: 13.17

Step by Step Solution

  1. Step 1: Write the proportion equation
    20.81 : 31.21 = 8.78 : x
  2. Step 2: Convert to fraction form
    20.81/31.21 = 8.78/x
  3. Step 3: Cross multiply
    20.81x = 31.21 × 8.78
  4. Step 4: Simplify right side
    20.81x = 273.98
  5. Step 5: Solve for x
    x = 273.98/20.81
  6. Step 6: Final answer
    x = 13.17

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