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Finding the Fourth Proportional to 86.21, 128.60 and 77.09

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Solution

The fourth proportional to 86.21, 128.60 and 77.09 is: 115.00

Step by Step Solution

  1. Step 1: Write the proportion equation
    86.21 : 128.60 = 77.09 : x
  2. Step 2: Convert to fraction form
    86.21/128.60 = 77.09/x
  3. Step 3: Cross multiply
    86.21x = 128.60 × 77.09
  4. Step 4: Simplify right side
    86.21x = 9,913.71
  5. Step 5: Solve for x
    x = 9,913.71/86.21
  6. Step 6: Final answer
    x = 115.00

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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.