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Finding the Fourth Proportional to 20.40, 28.16 and 15.72

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Solution

The fourth proportional to 20.40, 28.16 and 15.72 is: 21.70

Step by Step Solution

  1. Step 1: Write the proportion equation
    20.40 : 28.16 = 15.72 : x
  2. Step 2: Convert to fraction form
    20.40/28.16 = 15.72/x
  3. Step 3: Cross multiply
    20.40x = 28.16 × 15.72
  4. Step 4: Simplify right side
    20.40x = 442.64
  5. Step 5: Solve for x
    x = 442.64/20.40
  6. Step 6: Final answer
    x = 21.70

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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.