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Finding the Fourth Proportional to 100.40, 138.72 and 87.18

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Solution

The fourth proportional to 100.40, 138.72 and 87.18 is: 120.46

Step by Step Solution

  1. Step 1: Write the proportion equation
    100.40 : 138.72 = 87.18 : x
  2. Step 2: Convert to fraction form
    100.40/138.72 = 87.18/x
  3. Step 3: Cross multiply
    100.40x = 138.72 × 87.18
  4. Step 4: Simplify right side
    100.40x = 12,093.61
  5. Step 5: Solve for x
    x = 12,093.61/100.40
  6. Step 6: Final answer
    x = 120.46

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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.