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Finding the Fourth Proportional to 85.40, 128.20 and 72

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Solution

The fourth proportional to 85.40, 128.20 and 72 is: 108.08

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.40 : 128.20 = 72 : x
  2. Step 2: Convert to fraction form
    85.40/128.20 = 72/x
  3. Step 3: Cross multiply
    85.40x = 128.20 × 72
  4. Step 4: Simplify right side
    85.40x = 9,230.40
  5. Step 5: Solve for x
    x = 9,230.40/85.40
  6. Step 6: Final answer
    x = 108.08

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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.