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Finding the Fourth Proportional to 128.42, 177.21 and 86.99

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Solution

The fourth proportional to 128.42, 177.21 and 86.99 is: 120.04

Step by Step Solution

  1. Step 1: Write the proportion equation
    128.42 : 177.21 = 86.99 : x
  2. Step 2: Convert to fraction form
    128.42/177.21 = 86.99/x
  3. Step 3: Cross multiply
    128.42x = 177.21 × 86.99
  4. Step 4: Simplify right side
    128.42x = 15,415.50
  5. Step 5: Solve for x
    x = 15,415.50/128.42
  6. Step 6: Final answer
    x = 120.04

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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.