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Finding the Fourth Proportional to 809.40, 1,215.15 and 420.21

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Solution

The fourth proportional to 809.40, 1,215.15 and 420.21 is: 630.86

Step by Step Solution

  1. Step 1: Write the proportion equation
    809.40 : 1,215.15 = 420.21 : x
  2. Step 2: Convert to fraction form
    809.40/1,215.15 = 420.21/x
  3. Step 3: Cross multiply
    809.40x = 1,215.15 × 420.21
  4. Step 4: Simplify right side
    809.40x = 510,618.18
  5. Step 5: Solve for x
    x = 510,618.18/809.40
  6. Step 6: Final answer
    x = 630.86

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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.