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Finding the Fourth Proportional to 1,390.78, 1,919.28 and 769.78

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Solution

The fourth proportional to 1,390.78, 1,919.28 and 769.78 is: 1,062.30

Step by Step Solution

  1. Step 1: Write the proportion equation
    1,390.78 : 1,919.28 = 769.78 : x
  2. Step 2: Convert to fraction form
    1,390.78/1,919.28 = 769.78/x
  3. Step 3: Cross multiply
    1,390.78x = 1,919.28 × 769.78
  4. Step 4: Simplify right side
    1,390.78x = 1,477,423.36
  5. Step 5: Solve for x
    x = 1,477,423.36/1,390.78
  6. Step 6: Final answer
    x = 1,062.30

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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.