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Finding the Fourth Proportional to 21, 28.79 and 19.78

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Solution

The fourth proportional to 21, 28.79 and 19.78 is: 27.12

Step by Step Solution

  1. Step 1: Write the proportion equation
    21 : 28.79 = 19.78 : x
  2. Step 2: Convert to fraction form
    21/28.79 = 19.78/x
  3. Step 3: Cross multiply
    21x = 28.79 × 19.78
  4. Step 4: Simplify right side
    21x = 569.47
  5. Step 5: Solve for x
    x = 569.47/21
  6. Step 6: Final answer
    x = 27.12

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Why These Related Problems?

These problems maintain the same ratio (1.37) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.