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Finding the Fourth Proportional to 1,328.05, 1,991.40 and 780.40

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Solution

The fourth proportional to 1,328.05, 1,991.40 and 780.40 is: 1,170.20

Step by Step Solution

  1. Step 1: Write the proportion equation
    1,328.05 : 1,991.40 = 780.40 : x
  2. Step 2: Convert to fraction form
    1,328.05/1,991.40 = 780.40/x
  3. Step 3: Cross multiply
    1,328.05x = 1,991.40 × 780.40
  4. Step 4: Simplify right side
    1,328.05x = 1,554,088.56
  5. Step 5: Solve for x
    x = 1,554,088.56/1,328.05
  6. Step 6: Final answer
    x = 1,170.20

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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.