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Finding the Fourth Proportional to 142.40, 213.60 and 78.40

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Solution

The fourth proportional to 142.40, 213.60 and 78.40 is: 117.60

Step by Step Solution

  1. Step 1: Write the proportion equation
    142.40 : 213.60 = 78.40 : x
  2. Step 2: Convert to fraction form
    142.40/213.60 = 78.40/x
  3. Step 3: Cross multiply
    142.40x = 213.60 × 78.40
  4. Step 4: Simplify right side
    142.40x = 16,746.24
  5. Step 5: Solve for x
    x = 16,746.24/142.40
  6. Step 6: Final answer
    x = 117.60

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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.