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Finding the Fourth Proportional to 78, 107.64 and 61.68

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Solution

The fourth proportional to 78, 107.64 and 61.68 is: 85.12

Step by Step Solution

  1. Step 1: Write the proportion equation
    78 : 107.64 = 61.68 : x
  2. Step 2: Convert to fraction form
    78/107.64 = 61.68/x
  3. Step 3: Cross multiply
    78x = 107.64 × 61.68
  4. Step 4: Simplify right side
    78x = 6,639.24
  5. Step 5: Solve for x
    x = 6,639.24/78
  6. Step 6: Final answer
    x = 85.12

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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.