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Finding the Fourth Proportional to 85.45, 128.20 and 31.35

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Solution

The fourth proportional to 85.45, 128.20 and 31.35 is: 47.03

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.45 : 128.20 = 31.35 : x
  2. Step 2: Convert to fraction form
    85.45/128.20 = 31.35/x
  3. Step 3: Cross multiply
    85.45x = 128.20 × 31.35
  4. Step 4: Simplify right side
    85.45x = 4,019.07
  5. Step 5: Solve for x
    x = 4,019.07/85.45
  6. Step 6: Final answer
    x = 47.03

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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.