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Finding the Fourth Proportional to 918.78, 1,378.53 and 431.70

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Solution

The fourth proportional to 918.78, 1,378.53 and 431.70 is: 647.72

Step by Step Solution

  1. Step 1: Write the proportion equation
    918.78 : 1,378.53 = 431.70 : x
  2. Step 2: Convert to fraction form
    918.78/1,378.53 = 431.70/x
  3. Step 3: Cross multiply
    918.78x = 1,378.53 × 431.70
  4. Step 4: Simplify right side
    918.78x = 595,111.40
  5. Step 5: Solve for x
    x = 595,111.40/918.78
  6. Step 6: Final answer
    x = 647.72

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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.