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Finding the Fourth Proportional to 128.40, 172.80 and 128.40

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Solution

The fourth proportional to 128.40, 172.80 and 128.40 is: 172.80

Step by Step Solution

  1. Step 1: Write the proportion equation
    128.40 : 172.80 = 128.40 : x
  2. Step 2: Convert to fraction form
    128.40/172.80 = 128.40/x
  3. Step 3: Cross multiply
    128.40x = 172.80 × 128.40
  4. Step 4: Simplify right side
    128.40x = 22,187.52
  5. Step 5: Solve for x
    x = 22,187.52/128.40
  6. Step 6: Final answer
    x = 172.80

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Why These Related Problems?

These problems maintain the same ratio (1.35) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.