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Finding the Fourth Proportional to 831.68, 1,247.20 and 420

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Solution

The fourth proportional to 831.68, 1,247.20 and 420 is: 629.84

Step by Step Solution

  1. Step 1: Write the proportion equation
    831.68 : 1,247.20 = 420 : x
  2. Step 2: Convert to fraction form
    831.68/1,247.20 = 420/x
  3. Step 3: Cross multiply
    831.68x = 1,247.20 × 420
  4. Step 4: Simplify right side
    831.68x = 523,824
  5. Step 5: Solve for x
    x = 523,824/831.68
  6. Step 6: Final answer
    x = 629.84

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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.