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Finding the Fourth Proportional to 839.80, 1,259.70 and 428.80

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Solution

The fourth proportional to 839.80, 1,259.70 and 428.80 is: 643.20

Step by Step Solution

  1. Step 1: Write the proportion equation
    839.80 : 1,259.70 = 428.80 : x
  2. Step 2: Convert to fraction form
    839.80/1,259.70 = 428.80/x
  3. Step 3: Cross multiply
    839.80x = 1,259.70 × 428.80
  4. Step 4: Simplify right side
    839.80x = 540,159.36
  5. Step 5: Solve for x
    x = 540,159.36/839.80
  6. Step 6: Final answer
    x = 643.20

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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.