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Finding the Fourth Proportional to 21.31, 31.96 and 7.80

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Solution

The fourth proportional to 21.31, 31.96 and 7.80 is: 11.69

Step by Step Solution

  1. Step 1: Write the proportion equation
    21.31 : 31.96 = 7.80 : x
  2. Step 2: Convert to fraction form
    21.31/31.96 = 7.80/x
  3. Step 3: Cross multiply
    21.31x = 31.96 × 7.80
  4. Step 4: Simplify right side
    21.31x = 249.18
  5. Step 5: Solve for x
    x = 249.18/21.31
  6. Step 6: Final answer
    x = 11.69

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