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Finding the Fourth Proportional to 780.39, 1,078.47 and 640.28

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Solution

The fourth proportional to 780.39, 1,078.47 and 640.28 is: 884.85

Step by Step Solution

  1. Step 1: Write the proportion equation
    780.39 : 1,078.47 = 640.28 : x
  2. Step 2: Convert to fraction form
    780.39/1,078.47 = 640.28/x
  3. Step 3: Cross multiply
    780.39x = 1,078.47 × 640.28
  4. Step 4: Simplify right side
    780.39x = 690,525.47
  5. Step 5: Solve for x
    x = 690,525.47/780.39
  6. Step 6: Final answer
    x = 884.85

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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.