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Finding the Fourth Proportional to 21.72, 30 and 21.40

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Solution

The fourth proportional to 21.72, 30 and 21.40 is: 29.56

Step by Step Solution

  1. Step 1: Write the proportion equation
    21.72 : 30 = 21.40 : x
  2. Step 2: Convert to fraction form
    21.72/30 = 21.40/x
  3. Step 3: Cross multiply
    21.72x = 30 × 21.40
  4. Step 4: Simplify right side
    21.72x = 642
  5. Step 5: Solve for x
    x = 642/21.72
  6. Step 6: Final answer
    x = 29.56

Related Problems

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Similar ratio
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1.5x scale

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.