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Finding the Fourth Proportional to 90.40, 135.40 and 78.40

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Solution

The fourth proportional to 90.40, 135.40 and 78.40 is: 117.43

Step by Step Solution

  1. Step 1: Write the proportion equation
    90.40 : 135.40 = 78.40 : x
  2. Step 2: Convert to fraction form
    90.40/135.40 = 78.40/x
  3. Step 3: Cross multiply
    90.40x = 135.40 × 78.40
  4. Step 4: Simplify right side
    90.40x = 10,615.36
  5. Step 5: Solve for x
    x = 10,615.36/90.40
  6. Step 6: Final answer
    x = 117.43

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Why These Related Problems?

These problems maintain the same ratio (1.50) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.