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Finding the Fourth Proportional to 85.90, 128.80 and 45.31

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Solution

The fourth proportional to 85.90, 128.80 and 45.31 is: 67.93

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.90 : 128.80 = 45.31 : x
  2. Step 2: Convert to fraction form
    85.90/128.80 = 45.31/x
  3. Step 3: Cross multiply
    85.90x = 128.80 × 45.31
  4. Step 4: Simplify right side
    85.90x = 5,835.06
  5. Step 5: Solve for x
    x = 5,835.06/85.90
  6. Step 6: Final answer
    x = 67.93

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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.