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Finding the Fourth Proportional to 689.76, 1,039.94 and 642.78

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Solution

The fourth proportional to 689.76, 1,039.94 and 642.78 is: 969.10

Step by Step Solution

  1. Step 1: Write the proportion equation
    689.76 : 1,039.94 = 642.78 : x
  2. Step 2: Convert to fraction form
    689.76/1,039.94 = 642.78/x
  3. Step 3: Cross multiply
    689.76x = 1,039.94 × 642.78
  4. Step 4: Simplify right side
    689.76x = 668,449.42
  5. Step 5: Solve for x
    x = 668,449.42/689.76
  6. Step 6: Final answer
    x = 969.10

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Why These Related Problems?

These problems maintain the same ratio (1.51) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.