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Finding the Fourth Proportional to 813.20, 1,121.85 and 639.05

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Solution

The fourth proportional to 813.20, 1,121.85 and 639.05 is: 881.60

Step by Step Solution

  1. Step 1: Write the proportion equation
    813.20 : 1,121.85 = 639.05 : x
  2. Step 2: Convert to fraction form
    813.20/1,121.85 = 639.05/x
  3. Step 3: Cross multiply
    813.20x = 1,121.85 × 639.05
  4. Step 4: Simplify right side
    813.20x = 716,918.24
  5. Step 5: Solve for x
    x = 716,918.24/813.20
  6. Step 6: Final answer
    x = 881.60

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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.