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Finding the Fourth Proportional to 1,280.78, 1,921.20 and 664.40

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Solution

The fourth proportional to 1,280.78, 1,921.20 and 664.40 is: 996.62

Step by Step Solution

  1. Step 1: Write the proportion equation
    1,280.78 : 1,921.20 = 664.40 : x
  2. Step 2: Convert to fraction form
    1,280.78/1,921.20 = 664.40/x
  3. Step 3: Cross multiply
    1,280.78x = 1,921.20 × 664.40
  4. Step 4: Simplify right side
    1,280.78x = 1,276,445.28
  5. Step 5: Solve for x
    x = 1,276,445.28/1,280.78
  6. Step 6: Final answer
    x = 996.62

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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.