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Finding the Fourth Proportional to 21, 31.50 and 20.78

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Solution

The fourth proportional to 21, 31.50 and 20.78 is: 31.16

Step by Step Solution

  1. Step 1: Write the proportion equation
    21 : 31.50 = 20.78 : x
  2. Step 2: Convert to fraction form
    21/31.50 = 20.78/x
  3. Step 3: Cross multiply
    21x = 31.50 × 20.78
  4. Step 4: Simplify right side
    21x = 654.41
  5. Step 5: Solve for x
    x = 654.41/21
  6. Step 6: Final answer
    x = 31.16

Related Problems

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Half scale
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Double scale
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Similar ratio
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1.5x scale

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.