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Finding the Fourth Proportional to 85.79, 129.20 and 78.64

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Solution

The fourth proportional to 85.79, 129.20 and 78.64 is: 118.42

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.79 : 129.20 = 78.64 : x
  2. Step 2: Convert to fraction form
    85.79/129.20 = 78.64/x
  3. Step 3: Cross multiply
    85.79x = 129.20 × 78.64
  4. Step 4: Simplify right side
    85.79x = 10,159.57
  5. Step 5: Solve for x
    x = 10,159.57/85.79
  6. Step 6: Final answer
    x = 118.42

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Why These Related Problems?

These problems maintain the same ratio (1.51) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.