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Finding the Fourth Proportional to 821.20, 1,231.80 and 728.40

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Solution

The fourth proportional to 821.20, 1,231.80 and 728.40 is: 1,092.60

Step by Step Solution

  1. Step 1: Write the proportion equation
    821.20 : 1,231.80 = 728.40 : x
  2. Step 2: Convert to fraction form
    821.20/1,231.80 = 728.40/x
  3. Step 3: Cross multiply
    821.20x = 1,231.80 × 728.40
  4. Step 4: Simplify right side
    821.20x = 897,243.12
  5. Step 5: Solve for x
    x = 897,243.12/821.20
  6. Step 6: Final answer
    x = 1,092.60

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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.