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Finding the Fourth Proportional to 861.21, 1,291.16 and 428.67

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Solution

The fourth proportional to 861.21, 1,291.16 and 428.67 is: 642.68

Step by Step Solution

  1. Step 1: Write the proportion equation
    861.21 : 1,291.16 = 428.67 : x
  2. Step 2: Convert to fraction form
    861.21/1,291.16 = 428.67/x
  3. Step 3: Cross multiply
    861.21x = 1,291.16 × 428.67
  4. Step 4: Simplify right side
    861.21x = 553,482.63
  5. Step 5: Solve for x
    x = 553,482.63/861.21
  6. Step 6: Final answer
    x = 642.68

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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.