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Finding the Fourth Proportional to 21.12, 31.86 and 20.28

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Solution

The fourth proportional to 21.12, 31.86 and 20.28 is: 30.59

Step by Step Solution

  1. Step 1: Write the proportion equation
    21.12 : 31.86 = 20.28 : x
  2. Step 2: Convert to fraction form
    21.12/31.86 = 20.28/x
  3. Step 3: Cross multiply
    21.12x = 31.86 × 20.28
  4. Step 4: Simplify right side
    21.12x = 646.12
  5. Step 5: Solve for x
    x = 646.12/21.12
  6. Step 6: Final answer
    x = 30.59

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Why These Related Problems?

These problems maintain the same ratio (1.51) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.