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Finding the Fourth Proportional to 15.90, 21.90 and 13.15

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Solution

The fourth proportional to 15.90, 21.90 and 13.15 is: 18.11

Step by Step Solution

  1. Step 1: Write the proportion equation
    15.90 : 21.90 = 13.15 : x
  2. Step 2: Convert to fraction form
    15.90/21.90 = 13.15/x
  3. Step 3: Cross multiply
    15.90x = 21.90 × 13.15
  4. Step 4: Simplify right side
    15.90x = 287.99
  5. Step 5: Solve for x
    x = 287.99/15.90
  6. Step 6: Final answer
    x = 18.11

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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.