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Finding the Fourth Proportional to 65.78, 90.70 and 39.90

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Solution

The fourth proportional to 65.78, 90.70 and 39.90 is: 55.02

Step by Step Solution

  1. Step 1: Write the proportion equation
    65.78 : 90.70 = 39.90 : x
  2. Step 2: Convert to fraction form
    65.78/90.70 = 39.90/x
  3. Step 3: Cross multiply
    65.78x = 90.70 × 39.90
  4. Step 4: Simplify right side
    65.78x = 3,618.93
  5. Step 5: Solve for x
    x = 3,618.93/65.78
  6. Step 6: Final answer
    x = 55.02

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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.