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Finding the Fourth Proportional to 1,390.76, 1,919.36 and 831.40

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Solution

The fourth proportional to 1,390.76, 1,919.36 and 831.40 is: 1,147.40

Step by Step Solution

  1. Step 1: Write the proportion equation
    1,390.76 : 1,919.36 = 831.40 : x
  2. Step 2: Convert to fraction form
    1,390.76/1,919.36 = 831.40/x
  3. Step 3: Cross multiply
    1,390.76x = 1,919.36 × 831.40
  4. Step 4: Simplify right side
    1,390.76x = 1,595,755.90
  5. Step 5: Solve for x
    x = 1,595,755.90/1,390.76
  6. Step 6: Final answer
    x = 1,147.40

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Half scale
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Double scale
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1.5x scale

Why These Related Problems?

These problems maintain the same ratio (1.38) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.