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Finding the Fourth Proportional to 100.78, 139.12 and 76.28

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Solution

The fourth proportional to 100.78, 139.12 and 76.28 is: 105.29

Step by Step Solution

  1. Step 1: Write the proportion equation
    100.78 : 139.12 = 76.28 : x
  2. Step 2: Convert to fraction form
    100.78/139.12 = 76.28/x
  3. Step 3: Cross multiply
    100.78x = 139.12 × 76.28
  4. Step 4: Simplify right side
    100.78x = 10,611.19
  5. Step 5: Solve for x
    x = 10,611.19/100.78
  6. Step 6: Final answer
    x = 105.29

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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.