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Finding the Fourth Proportional to 30.78, 42.48 and 21.12

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Solution

The fourth proportional to 30.78, 42.48 and 21.12 is: 29.15

Step by Step Solution

  1. Step 1: Write the proportion equation
    30.78 : 42.48 = 21.12 : x
  2. Step 2: Convert to fraction form
    30.78/42.48 = 21.12/x
  3. Step 3: Cross multiply
    30.78x = 42.48 × 21.12
  4. Step 4: Simplify right side
    30.78x = 897.18
  5. Step 5: Solve for x
    x = 897.18/30.78
  6. Step 6: Final answer
    x = 29.15

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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.