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Finding the Fourth Proportional to 428.78, 643.37 and 212.51

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Solution

The fourth proportional to 428.78, 643.37 and 212.51 is: 318.86

Step by Step Solution

  1. Step 1: Write the proportion equation
    428.78 : 643.37 = 212.51 : x
  2. Step 2: Convert to fraction form
    428.78/643.37 = 212.51/x
  3. Step 3: Cross multiply
    428.78x = 643.37 × 212.51
  4. Step 4: Simplify right side
    428.78x = 136,718.28
  5. Step 5: Solve for x
    x = 136,718.28/428.78
  6. Step 6: Final answer
    x = 318.86

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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.