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Finding the Fourth Proportional to 121.99, 168.40 and 78.39

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Solution

The fourth proportional to 121.99, 168.40 and 78.39 is: 108.21

Step by Step Solution

  1. Step 1: Write the proportion equation
    121.99 : 168.40 = 78.39 : x
  2. Step 2: Convert to fraction form
    121.99/168.40 = 78.39/x
  3. Step 3: Cross multiply
    121.99x = 168.40 × 78.39
  4. Step 4: Simplify right side
    121.99x = 13,200.88
  5. Step 5: Solve for x
    x = 13,200.88/121.99
  6. Step 6: Final answer
    x = 108.21

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Why These Related Problems?

These problems maintain the same ratio (1.38) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.