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Finding the Fourth Proportional to 21.20, 31.80 and 13.10

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Solution

The fourth proportional to 21.20, 31.80 and 13.10 is: 19.64

Step by Step Solution

  1. Step 1: Write the proportion equation
    21.20 : 31.80 = 13.10 : x
  2. Step 2: Convert to fraction form
    21.20/31.80 = 13.10/x
  3. Step 3: Cross multiply
    21.20x = 31.80 × 13.10
  4. Step 4: Simplify right side
    21.20x = 416.42
  5. Step 5: Solve for x
    x = 416.42/21.20
  6. Step 6: Final answer
    x = 19.64

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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.