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Finding the Fourth Proportional to 1,287.70, 1,931.55 and 639.70

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Solution

The fourth proportional to 1,287.70, 1,931.55 and 639.70 is: 959.55

Step by Step Solution

  1. Step 1: Write the proportion equation
    1,287.70 : 1,931.55 = 639.70 : x
  2. Step 2: Convert to fraction form
    1,287.70/1,931.55 = 639.70/x
  3. Step 3: Cross multiply
    1,287.70x = 1,931.55 × 639.70
  4. Step 4: Simplify right side
    1,287.70x = 1,235,612.54
  5. Step 5: Solve for x
    x = 1,235,612.54/1,287.70
  6. Step 6: Final answer
    x = 959.55

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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.