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Finding the Fourth Proportional to 21.18, 31.78 and 13.18

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Solution

The fourth proportional to 21.18, 31.78 and 13.18 is: 19.78

Step by Step Solution

  1. Step 1: Write the proportion equation
    21.18 : 31.78 = 13.18 : x
  2. Step 2: Convert to fraction form
    21.18/31.78 = 13.18/x
  3. Step 3: Cross multiply
    21.18x = 31.78 × 13.18
  4. Step 4: Simplify right side
    21.18x = 418.86
  5. Step 5: Solve for x
    x = 418.86/21.18
  6. Step 6: Final answer
    x = 19.78

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Why These Related Problems?

These problems maintain the same ratio (1.50) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.