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Finding the Fourth Proportional to 261.28, 390.85 and 215.11

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Solution

The fourth proportional to 261.28, 390.85 and 215.11 is: 321.78

Step by Step Solution

  1. Step 1: Write the proportion equation
    261.28 : 390.85 = 215.11 : x
  2. Step 2: Convert to fraction form
    261.28/390.85 = 215.11/x
  3. Step 3: Cross multiply
    261.28x = 390.85 × 215.11
  4. Step 4: Simplify right side
    261.28x = 84,075.74
  5. Step 5: Solve for x
    x = 84,075.74/261.28
  6. Step 6: Final answer
    x = 321.78

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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.