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Finding the Fourth Proportional to 86.10, 128.40 and 77

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Solution

The fourth proportional to 86.10, 128.40 and 77 is: 114.83

Step by Step Solution

  1. Step 1: Write the proportion equation
    86.10 : 128.40 = 77 : x
  2. Step 2: Convert to fraction form
    86.10/128.40 = 77/x
  3. Step 3: Cross multiply
    86.10x = 128.40 × 77
  4. Step 4: Simplify right side
    86.10x = 9,886.80
  5. Step 5: Solve for x
    x = 9,886.80/86.10
  6. Step 6: Final answer
    x = 114.83

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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.