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Finding the Fourth Proportional to 781.40, 1,172.11 and 261.40

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Solution

The fourth proportional to 781.40, 1,172.11 and 261.40 is: 392.10

Step by Step Solution

  1. Step 1: Write the proportion equation
    781.40 : 1,172.11 = 261.40 : x
  2. Step 2: Convert to fraction form
    781.40/1,172.11 = 261.40/x
  3. Step 3: Cross multiply
    781.40x = 1,172.11 × 261.40
  4. Step 4: Simplify right side
    781.40x = 306,389.55
  5. Step 5: Solve for x
    x = 306,389.55/781.40
  6. Step 6: Final answer
    x = 392.10

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Why These Related Problems?

These problems maintain the same ratio (1.50) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.