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Finding the Fourth Proportional to 1,390.64, 2,085.21 and 687.74

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Solution

The fourth proportional to 1,390.64, 2,085.21 and 687.74 is: 1,031.24

Step by Step Solution

  1. Step 1: Write the proportion equation
    1,390.64 : 2,085.21 = 687.74 : x
  2. Step 2: Convert to fraction form
    1,390.64/2,085.21 = 687.74/x
  3. Step 3: Cross multiply
    1,390.64x = 2,085.21 × 687.74
  4. Step 4: Simplify right side
    1,390.64x = 1,434,071.90
  5. Step 5: Solve for x
    x = 1,434,071.90/1,390.64
  6. Step 6: Final answer
    x = 1,031.24

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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.