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Finding the Fourth Proportional to 31, 42.78 and 20.09

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Solution

The fourth proportional to 31, 42.78 and 20.09 is: 27.72

Step by Step Solution

  1. Step 1: Write the proportion equation
    31 : 42.78 = 20.09 : x
  2. Step 2: Convert to fraction form
    31/42.78 = 20.09/x
  3. Step 3: Cross multiply
    31x = 42.78 × 20.09
  4. Step 4: Simplify right side
    31x = 859.24
  5. Step 5: Solve for x
    x = 859.24/31
  6. Step 6: Final answer
    x = 27.72

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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.