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Finding the Fourth Proportional to 21.79, 30.05 and 15.65

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Solution

The fourth proportional to 21.79, 30.05 and 15.65 is: 21.58

Step by Step Solution

  1. Step 1: Write the proportion equation
    21.79 : 30.05 = 15.65 : x
  2. Step 2: Convert to fraction form
    21.79/30.05 = 15.65/x
  3. Step 3: Cross multiply
    21.79x = 30.05 × 15.65
  4. Step 4: Simplify right side
    21.79x = 470.20
  5. Step 5: Solve for x
    x = 470.20/21.79
  6. Step 6: Final answer
    x = 21.58

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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.