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Finding the Third Proportional to 12 and 21

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Solution

The third proportional to 12 and 21 is: 36.75

Step by Step Solution

  1. Step 1: Write the proportion equation
    12 : 21 = 21 : x
  2. Step 2: Convert to fraction form
    12/21 = 21/x
  3. Step 3: Cross multiply
    12x = 21 × 21
  4. Step 4: Simplify right side
    12x = 441
  5. Step 5: Solve for x
    x = 441/12
  6. Step 6: Final answer
    x = 36.75

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1.5x scale

Why These Related Problems?

These problems maintain the same ratio (1.75) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.