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Finding the Fourth Proportional to 31.20, 42.81 and 30.78

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Solution

The fourth proportional to 31.20, 42.81 and 30.78 is: 42.23

Step by Step Solution

  1. Step 1: Write the proportion equation
    31.20 : 42.81 = 30.78 : x
  2. Step 2: Convert to fraction form
    31.20/42.81 = 30.78/x
  3. Step 3: Cross multiply
    31.20x = 42.81 × 30.78
  4. Step 4: Simplify right side
    31.20x = 1,317.69
  5. Step 5: Solve for x
    x = 1,317.69/31.20
  6. Step 6: Final answer
    x = 42.23

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Why These Related Problems?

These problems maintain the same ratio (1.37) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.