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Finding the Fourth Proportional to 861.39, 1,291.88 and 428.45

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Solution

The fourth proportional to 861.39, 1,291.88 and 428.45 is: 642.57

Step by Step Solution

  1. Step 1: Write the proportion equation
    861.39 : 1,291.88 = 428.45 : x
  2. Step 2: Convert to fraction form
    861.39/1,291.88 = 428.45/x
  3. Step 3: Cross multiply
    861.39x = 1,291.88 × 428.45
  4. Step 4: Simplify right side
    861.39x = 553,500.60
  5. Step 5: Solve for x
    x = 553,500.60/861.39
  6. Step 6: Final answer
    x = 642.57

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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.