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Finding the Fourth Proportional to 831.90, 1,247.90 and 420.55

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Solution

The fourth proportional to 831.90, 1,247.90 and 420.55 is: 630.85

Step by Step Solution

  1. Step 1: Write the proportion equation
    831.90 : 1,247.90 = 420.55 : x
  2. Step 2: Convert to fraction form
    831.90/1,247.90 = 420.55/x
  3. Step 3: Cross multiply
    831.90x = 1,247.90 × 420.55
  4. Step 4: Simplify right side
    831.90x = 524,804.35
  5. Step 5: Solve for x
    x = 524,804.35/831.90
  6. Step 6: Final answer
    x = 630.85

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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.