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Finding the Fourth Proportional to 921.20, 1,389.10 and 820.40

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Solution

The fourth proportional to 921.20, 1,389.10 and 820.40 is: 1,237.10

Step by Step Solution

  1. Step 1: Write the proportion equation
    921.20 : 1,389.10 = 820.40 : x
  2. Step 2: Convert to fraction form
    921.20/1,389.10 = 820.40/x
  3. Step 3: Cross multiply
    921.20x = 1,389.10 × 820.40
  4. Step 4: Simplify right side
    921.20x = 1,139,617.64
  5. Step 5: Solve for x
    x = 1,139,617.64/921.20
  6. Step 6: Final answer
    x = 1,237.10

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1.5x scale

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.