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Finding the Third Proportional to 1,990 and 3,920

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Solution

The third proportional to 1,990 and 3,920 is: 7,721.81

Step by Step Solution

  1. Step 1: Write the proportion equation
    1,990 : 3,920 = 3,920 : x
  2. Step 2: Convert to fraction form
    1,990/3,920 = 3,920/x
  3. Step 3: Cross multiply
    1,990x = 3,920 × 3,920
  4. Step 4: Simplify right side
    1,990x = 15,366,400
  5. Step 5: Solve for x
    x = 15,366,400/1,990
  6. Step 6: Final answer
    x = 7,721.81

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Why These Related Problems?

These problems maintain the same ratio (1.97) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.