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Finding the Fourth Proportional to 812.40, 1,216.80 and 721.20

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Solution

The fourth proportional to 812.40, 1,216.80 and 721.20 is: 1,080.20

Step by Step Solution

  1. Step 1: Write the proportion equation
    812.40 : 1,216.80 = 721.20 : x
  2. Step 2: Convert to fraction form
    812.40/1,216.80 = 721.20/x
  3. Step 3: Cross multiply
    812.40x = 1,216.80 × 721.20
  4. Step 4: Simplify right side
    812.40x = 877,556.16
  5. Step 5: Solve for x
    x = 877,556.16/812.40
  6. Step 6: Final answer
    x = 1,080.20

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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.