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Finding the Fourth Proportional to 87.81, 121.20 and 56.78

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Solution

The fourth proportional to 87.81, 121.20 and 56.78 is: 78.36

Step by Step Solution

  1. Step 1: Write the proportion equation
    87.81 : 121.20 = 56.78 : x
  2. Step 2: Convert to fraction form
    87.81/121.20 = 56.78/x
  3. Step 3: Cross multiply
    87.81x = 121.20 × 56.78
  4. Step 4: Simplify right side
    87.81x = 6,881.13
  5. Step 5: Solve for x
    x = 6,881.13/87.81
  6. Step 6: Final answer
    x = 78.36

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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.