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Finding the Fourth Proportional to 678.80, 1,018.20 and 405.20

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Solution

The fourth proportional to 678.80, 1,018.20 and 405.20 is: 607.80

Step by Step Solution

  1. Step 1: Write the proportion equation
    678.80 : 1,018.20 = 405.20 : x
  2. Step 2: Convert to fraction form
    678.80/1,018.20 = 405.20/x
  3. Step 3: Cross multiply
    678.80x = 1,018.20 × 405.20
  4. Step 4: Simplify right side
    678.80x = 412,574.64
  5. Step 5: Solve for x
    x = 412,574.64/678.80
  6. Step 6: Final answer
    x = 607.80

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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.