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Finding the Fourth Proportional to 1,292.20, 1,938.78 and 643

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Solution

The fourth proportional to 1,292.20, 1,938.78 and 643 is: 964.74

Step by Step Solution

  1. Step 1: Write the proportion equation
    1,292.20 : 1,938.78 = 643 : x
  2. Step 2: Convert to fraction form
    1,292.20/1,938.78 = 643/x
  3. Step 3: Cross multiply
    1,292.20x = 1,938.78 × 643
  4. Step 4: Simplify right side
    1,292.20x = 1,246,635.54
  5. Step 5: Solve for x
    x = 1,246,635.54/1,292.20
  6. Step 6: Final answer
    x = 964.74

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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.