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Finding the Fourth Proportional to 831.42, 1,247.91 and 420.85

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Solution

The fourth proportional to 831.42, 1,247.91 and 420.85 is: 631.66

Step by Step Solution

  1. Step 1: Write the proportion equation
    831.42 : 1,247.91 = 420.85 : x
  2. Step 2: Convert to fraction form
    831.42/1,247.91 = 420.85/x
  3. Step 3: Cross multiply
    831.42x = 1,247.91 × 420.85
  4. Step 4: Simplify right side
    831.42x = 525,175.89
  5. Step 5: Solve for x
    x = 525,175.89/831.42
  6. Step 6: Final answer
    x = 631.66

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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.