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Finding the Third Proportional to 15 and 21

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Solution

The third proportional to 15 and 21 is: 29.40

Step by Step Solution

  1. Step 1: Write the proportion equation
    15 : 21 = 21 : x
  2. Step 2: Convert to fraction form
    15/21 = 21/x
  3. Step 3: Cross multiply
    15x = 21 × 21
  4. Step 4: Simplify right side
    15x = 441
  5. Step 5: Solve for x
    x = 441/15
  6. Step 6: Final answer
    x = 29.40

Related Problems

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1.5x scale

Why These Related Problems?

These problems maintain the same ratio (1.40) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.