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Finding the Fourth Proportional to 21.18, 31.86 and 21

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Solution

The fourth proportional to 21.18, 31.86 and 21 is: 31.59

Step by Step Solution

  1. Step 1: Write the proportion equation
    21.18 : 31.86 = 21 : x
  2. Step 2: Convert to fraction form
    21.18/31.86 = 21/x
  3. Step 3: Cross multiply
    21.18x = 31.86 × 21
  4. Step 4: Simplify right side
    21.18x = 669.06
  5. Step 5: Solve for x
    x = 669.06/21.18
  6. Step 6: Final answer
    x = 31.59

Related Problems

Find fourth proportional to 10.59, 15.93 and 10.50
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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.