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Finding the Fourth Proportional to 428.48, 640.80 and 420.80

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Solution

The fourth proportional to 428.48, 640.80 and 420.80 is: 629.31

Step by Step Solution

  1. Step 1: Write the proportion equation
    428.48 : 640.80 = 420.80 : x
  2. Step 2: Convert to fraction form
    428.48/640.80 = 420.80/x
  3. Step 3: Cross multiply
    428.48x = 640.80 × 420.80
  4. Step 4: Simplify right side
    428.48x = 269,648.64
  5. Step 5: Solve for x
    x = 269,648.64/428.48
  6. Step 6: Final answer
    x = 629.31

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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.