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Finding the Fourth Proportional to 15.78, 21.78 and 9.31

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Solution

The fourth proportional to 15.78, 21.78 and 9.31 is: 12.85

Step by Step Solution

  1. Step 1: Write the proportion equation
    15.78 : 21.78 = 9.31 : x
  2. Step 2: Convert to fraction form
    15.78/21.78 = 9.31/x
  3. Step 3: Cross multiply
    15.78x = 21.78 × 9.31
  4. Step 4: Simplify right side
    15.78x = 202.81
  5. Step 5: Solve for x
    x = 202.81/15.78
  6. Step 6: Final answer
    x = 12.85

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Why These Related Problems?

These problems maintain the same ratio (1.38) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.