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Finding the Fourth Proportional to 428.99, 643.55 and 212.45

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Solution

The fourth proportional to 428.99, 643.55 and 212.45 is: 318.70

Step by Step Solution

  1. Step 1: Write the proportion equation
    428.99 : 643.55 = 212.45 : x
  2. Step 2: Convert to fraction form
    428.99/643.55 = 212.45/x
  3. Step 3: Cross multiply
    428.99x = 643.55 × 212.45
  4. Step 4: Simplify right side
    428.99x = 136,717.92
  5. Step 5: Solve for x
    x = 136,717.92/428.99
  6. Step 6: Final answer
    x = 318.70

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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.