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Finding the Fourth Proportional to 85.90, 128.70 and 53.80

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Solution

The fourth proportional to 85.90, 128.70 and 53.80 is: 80.61

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.90 : 128.70 = 53.80 : x
  2. Step 2: Convert to fraction form
    85.90/128.70 = 53.80/x
  3. Step 3: Cross multiply
    85.90x = 128.70 × 53.80
  4. Step 4: Simplify right side
    85.90x = 6,924.06
  5. Step 5: Solve for x
    x = 6,924.06/85.90
  6. Step 6: Final answer
    x = 80.61

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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.