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Finding the Fourth Proportional to 100.57, 138.74 and 78.40

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Solution

The fourth proportional to 100.57, 138.74 and 78.40 is: 108.16

Step by Step Solution

  1. Step 1: Write the proportion equation
    100.57 : 138.74 = 78.40 : x
  2. Step 2: Convert to fraction form
    100.57/138.74 = 78.40/x
  3. Step 3: Cross multiply
    100.57x = 138.74 × 78.40
  4. Step 4: Simplify right side
    100.57x = 10,877.29
  5. Step 5: Solve for x
    x = 10,877.29/100.57
  6. Step 6: Final answer
    x = 108.16

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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.