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Finding the Fourth Proportional to 1,287.80, 1,931.70 and 639.80

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Solution

The fourth proportional to 1,287.80, 1,931.70 and 639.80 is: 959.70

Step by Step Solution

  1. Step 1: Write the proportion equation
    1,287.80 : 1,931.70 = 639.80 : x
  2. Step 2: Convert to fraction form
    1,287.80/1,931.70 = 639.80/x
  3. Step 3: Cross multiply
    1,287.80x = 1,931.70 × 639.80
  4. Step 4: Simplify right side
    1,287.80x = 1,235,901.66
  5. Step 5: Solve for x
    x = 1,235,901.66/1,287.80
  6. Step 6: Final answer
    x = 959.70

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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.