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Finding the Fourth Proportional to 15.78, 21.72 and 13.20

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Solution

The fourth proportional to 15.78, 21.72 and 13.20 is: 18.17

Step by Step Solution

  1. Step 1: Write the proportion equation
    15.78 : 21.72 = 13.20 : x
  2. Step 2: Convert to fraction form
    15.78/21.72 = 13.20/x
  3. Step 3: Cross multiply
    15.78x = 21.72 × 13.20
  4. Step 4: Simplify right side
    15.78x = 286.70
  5. Step 5: Solve for x
    x = 286.70/15.78
  6. Step 6: Final answer
    x = 18.17

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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.