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Finding the Fourth Proportional to 78.40, 108.80 and 72.64

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Solution

The fourth proportional to 78.40, 108.80 and 72.64 is: 100.81

Step by Step Solution

  1. Step 1: Write the proportion equation
    78.40 : 108.80 = 72.64 : x
  2. Step 2: Convert to fraction form
    78.40/108.80 = 72.64/x
  3. Step 3: Cross multiply
    78.40x = 108.80 × 72.64
  4. Step 4: Simplify right side
    78.40x = 7,903.23
  5. Step 5: Solve for x
    x = 7,903.23/78.40
  6. Step 6: Final answer
    x = 100.81

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Why These Related Problems?

These problems maintain the same ratio (1.39) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.