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Finding the Fourth Proportional to 138, 205.78 and 128.08

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Solution

The fourth proportional to 138, 205.78 and 128.08 is: 190.99

Step by Step Solution

  1. Step 1: Write the proportion equation
    138 : 205.78 = 128.08 : x
  2. Step 2: Convert to fraction form
    138/205.78 = 128.08/x
  3. Step 3: Cross multiply
    138x = 205.78 × 128.08
  4. Step 4: Simplify right side
    138x = 26,356.30
  5. Step 5: Solve for x
    x = 26,356.30/138
  6. Step 6: Final answer
    x = 190.99

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Why These Related Problems?

These problems maintain the same ratio (1.49) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.