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Finding the Fourth Proportional to 1,390.85, 1,919.19 and 831.21

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Solution

The fourth proportional to 1,390.85, 1,919.19 and 831.21 is: 1,146.97

Step by Step Solution

  1. Step 1: Write the proportion equation
    1,390.85 : 1,919.19 = 831.21 : x
  2. Step 2: Convert to fraction form
    1,390.85/1,919.19 = 831.21/x
  3. Step 3: Cross multiply
    1,390.85x = 1,919.19 × 831.21
  4. Step 4: Simplify right side
    1,390.85x = 1,595,256.64
  5. Step 5: Solve for x
    x = 1,595,256.64/1,390.85
  6. Step 6: Final answer
    x = 1,146.97

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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.