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Finding the Fourth Proportional to 1,391.42, 1,920 and 831.76

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Solution

The fourth proportional to 1,391.42, 1,920 and 831.76 is: 1,147.73

Step by Step Solution

  1. Step 1: Write the proportion equation
    1,391.42 : 1,920 = 831.76 : x
  2. Step 2: Convert to fraction form
    1,391.42/1,920 = 831.76/x
  3. Step 3: Cross multiply
    1,391.42x = 1,920 × 831.76
  4. Step 4: Simplify right side
    1,391.42x = 1,596,979.20
  5. Step 5: Solve for x
    x = 1,596,979.20/1,391.42
  6. Step 6: Final answer
    x = 1,147.73

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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.