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Finding the Fourth Proportional to 687.65, 1,031.90 and 428.16

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Solution

The fourth proportional to 687.65, 1,031.90 and 428.16 is: 642.50

Step by Step Solution

  1. Step 1: Write the proportion equation
    687.65 : 1,031.90 = 428.16 : x
  2. Step 2: Convert to fraction form
    687.65/1,031.90 = 428.16/x
  3. Step 3: Cross multiply
    687.65x = 1,031.90 × 428.16
  4. Step 4: Simplify right side
    687.65x = 441,813.90
  5. Step 5: Solve for x
    x = 441,813.90/687.65
  6. Step 6: Final answer
    x = 642.50

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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.