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Finding the Fourth Proportional to 861.78, 1,187.91 and 640.38

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Solution

The fourth proportional to 861.78, 1,187.91 and 640.38 is: 882.72

Step by Step Solution

  1. Step 1: Write the proportion equation
    861.78 : 1,187.91 = 640.38 : x
  2. Step 2: Convert to fraction form
    861.78/1,187.91 = 640.38/x
  3. Step 3: Cross multiply
    861.78x = 1,187.91 × 640.38
  4. Step 4: Simplify right side
    861.78x = 760,713.81
  5. Step 5: Solve for x
    x = 760,713.81/861.78
  6. Step 6: Final answer
    x = 882.72

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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.