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Finding the Fourth Proportional to 390.40, 538.70 and 215.72

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Solution

The fourth proportional to 390.40, 538.70 and 215.72 is: 297.66

Step by Step Solution

  1. Step 1: Write the proportion equation
    390.40 : 538.70 = 215.72 : x
  2. Step 2: Convert to fraction form
    390.40/538.70 = 215.72/x
  3. Step 3: Cross multiply
    390.40x = 538.70 × 215.72
  4. Step 4: Simplify right side
    390.40x = 116,208.36
  5. Step 5: Solve for x
    x = 116,208.36/390.40
  6. Step 6: Final answer
    x = 297.66

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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.