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Finding the Fourth Proportional to 100.40, 138.60 and 72.80

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Solution

The fourth proportional to 100.40, 138.60 and 72.80 is: 100.50

Step by Step Solution

  1. Step 1: Write the proportion equation
    100.40 : 138.60 = 72.80 : x
  2. Step 2: Convert to fraction form
    100.40/138.60 = 72.80/x
  3. Step 3: Cross multiply
    100.40x = 138.60 × 72.80
  4. Step 4: Simplify right side
    100.40x = 10,090.08
  5. Step 5: Solve for x
    x = 10,090.08/100.40
  6. Step 6: Final answer
    x = 100.50

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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.