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Finding the Fourth Proportional to 85.68, 128.36 and 47.21

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Solution

The fourth proportional to 85.68, 128.36 and 47.21 is: 70.72

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.68 : 128.36 = 47.21 : x
  2. Step 2: Convert to fraction form
    85.68/128.36 = 47.21/x
  3. Step 3: Cross multiply
    85.68x = 128.36 × 47.21
  4. Step 4: Simplify right side
    85.68x = 6,059.35
  5. Step 5: Solve for x
    x = 6,059.35/85.68
  6. Step 6: Final answer
    x = 70.72

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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.