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Finding the Fourth Proportional to 687.60, 1,031.40 and 620.40

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Solution

The fourth proportional to 687.60, 1,031.40 and 620.40 is: 930.60

Step by Step Solution

  1. Step 1: Write the proportion equation
    687.60 : 1,031.40 = 620.40 : x
  2. Step 2: Convert to fraction form
    687.60/1,031.40 = 620.40/x
  3. Step 3: Cross multiply
    687.60x = 1,031.40 × 620.40
  4. Step 4: Simplify right side
    687.60x = 639,880.56
  5. Step 5: Solve for x
    x = 639,880.56/687.60
  6. Step 6: Final answer
    x = 930.60

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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.