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Finding the Fourth Proportional to 90.99, 125.21 and 78.64

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Solution

The fourth proportional to 90.99, 125.21 and 78.64 is: 108.21

Step by Step Solution

  1. Step 1: Write the proportion equation
    90.99 : 125.21 = 78.64 : x
  2. Step 2: Convert to fraction form
    90.99/125.21 = 78.64/x
  3. Step 3: Cross multiply
    90.99x = 125.21 × 78.64
  4. Step 4: Simplify right side
    90.99x = 9,846.40
  5. Step 5: Solve for x
    x = 9,846.40/90.99
  6. Step 6: Final answer
    x = 108.21

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Why These Related Problems?

These problems maintain the same ratio (1.38) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.