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Finding the Fourth Proportional to 990.78, 1,485.86 and 405.78

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Solution

The fourth proportional to 990.78, 1,485.86 and 405.78 is: 608.54

Step by Step Solution

  1. Step 1: Write the proportion equation
    990.78 : 1,485.86 = 405.78 : x
  2. Step 2: Convert to fraction form
    990.78/1,485.86 = 405.78/x
  3. Step 3: Cross multiply
    990.78x = 1,485.86 × 405.78
  4. Step 4: Simplify right side
    990.78x = 602,930.24
  5. Step 5: Solve for x
    x = 602,930.24/990.78
  6. Step 6: Final answer
    x = 608.54

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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.