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Finding the Fourth Proportional to 78.40, 117.42 and 71.20

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Solution

The fourth proportional to 78.40, 117.42 and 71.20 is: 106.64

Step by Step Solution

  1. Step 1: Write the proportion equation
    78.40 : 117.42 = 71.20 : x
  2. Step 2: Convert to fraction form
    78.40/117.42 = 71.20/x
  3. Step 3: Cross multiply
    78.40x = 117.42 × 71.20
  4. Step 4: Simplify right side
    78.40x = 8,360.30
  5. Step 5: Solve for x
    x = 8,360.30/78.40
  6. Step 6: Final answer
    x = 106.64

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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.