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Finding the Third Proportional to 420 and 643.50

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Solution

The third proportional to 420 and 643.50 is: 985.93

Step by Step Solution

  1. Step 1: Write the proportion equation
    420 : 643.50 = 643.50 : x
  2. Step 2: Convert to fraction form
    420/643.50 = 643.50/x
  3. Step 3: Cross multiply
    420x = 643.50 × 643.50
  4. Step 4: Simplify right side
    420x = 414,092.25
  5. Step 5: Solve for x
    x = 414,092.25/420
  6. Step 6: Final answer
    x = 985.93

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Why These Related Problems?

These problems maintain the same ratio (1.53) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.