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Finding the Fourth Proportional to 85.79, 128.70 and 31.68

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Solution

The fourth proportional to 85.79, 128.70 and 31.68 is: 47.53

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.79 : 128.70 = 31.68 : x
  2. Step 2: Convert to fraction form
    85.79/128.70 = 31.68/x
  3. Step 3: Cross multiply
    85.79x = 128.70 × 31.68
  4. Step 4: Simplify right side
    85.79x = 4,077.22
  5. Step 5: Solve for x
    x = 4,077.22/85.79
  6. Step 6: Final answer
    x = 47.53

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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.