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Finding the Fourth Proportional to 1,389.78, 1,917.90 and 768.78

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Solution

The fourth proportional to 1,389.78, 1,917.90 and 768.78 is: 1,060.92

Step by Step Solution

  1. Step 1: Write the proportion equation
    1,389.78 : 1,917.90 = 768.78 : x
  2. Step 2: Convert to fraction form
    1,389.78/1,917.90 = 768.78/x
  3. Step 3: Cross multiply
    1,389.78x = 1,917.90 × 768.78
  4. Step 4: Simplify right side
    1,389.78x = 1,474,443.16
  5. Step 5: Solve for x
    x = 1,474,443.16/1,389.78
  6. Step 6: Final answer
    x = 1,060.92

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1.5x scale

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.