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Finding the Fourth Proportional to 100.64, 138.84 and 78.72

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Solution

The fourth proportional to 100.64, 138.84 and 78.72 is: 108.60

Step by Step Solution

  1. Step 1: Write the proportion equation
    100.64 : 138.84 = 78.72 : x
  2. Step 2: Convert to fraction form
    100.64/138.84 = 78.72/x
  3. Step 3: Cross multiply
    100.64x = 138.84 × 78.72
  4. Step 4: Simplify right side
    100.64x = 10,929.48
  5. Step 5: Solve for x
    x = 10,929.48/100.64
  6. Step 6: Final answer
    x = 108.60

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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.