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Finding the Fourth Proportional to 858.20, 1,287.70 and 642.20

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Solution

The fourth proportional to 858.20, 1,287.70 and 642.20 is: 963.60

Step by Step Solution

  1. Step 1: Write the proportion equation
    858.20 : 1,287.70 = 642.20 : x
  2. Step 2: Convert to fraction form
    858.20/1,287.70 = 642.20/x
  3. Step 3: Cross multiply
    858.20x = 1,287.70 × 642.20
  4. Step 4: Simplify right side
    858.20x = 826,960.94
  5. Step 5: Solve for x
    x = 826,960.94/858.20
  6. Step 6: Final answer
    x = 963.60

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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.