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Finding the Fourth Proportional to 85.77, 128.90 and 78.06

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Solution

The fourth proportional to 85.77, 128.90 and 78.06 is: 117.32

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.77 : 128.90 = 78.06 : x
  2. Step 2: Convert to fraction form
    85.77/128.90 = 78.06/x
  3. Step 3: Cross multiply
    85.77x = 128.90 × 78.06
  4. Step 4: Simplify right side
    85.77x = 10,062.72
  5. Step 5: Solve for x
    x = 10,062.72/85.77
  6. Step 6: Final answer
    x = 117.32

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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.