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Finding the Fourth Proportional to 715.50, 987.42 and 420.78

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Solution

The fourth proportional to 715.50, 987.42 and 420.78 is: 580.69

Step by Step Solution

  1. Step 1: Write the proportion equation
    715.50 : 987.42 = 420.78 : x
  2. Step 2: Convert to fraction form
    715.50/987.42 = 420.78/x
  3. Step 3: Cross multiply
    715.50x = 987.42 × 420.78
  4. Step 4: Simplify right side
    715.50x = 415,486.59
  5. Step 5: Solve for x
    x = 415,486.59/715.50
  6. Step 6: Final answer
    x = 580.69

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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.