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Finding the Fourth Proportional to 428.97, 643.60 and 212.40

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Solution

The fourth proportional to 428.97, 643.60 and 212.40 is: 318.67

Step by Step Solution

  1. Step 1: Write the proportion equation
    428.97 : 643.60 = 212.40 : x
  2. Step 2: Convert to fraction form
    428.97/643.60 = 212.40/x
  3. Step 3: Cross multiply
    428.97x = 643.60 × 212.40
  4. Step 4: Simplify right side
    428.97x = 136,700.91
  5. Step 5: Solve for x
    x = 136,700.91/428.97
  6. Step 6: Final answer
    x = 318.67

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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.