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Complete the series: 21, 20, 18, 15, 11, ______?

Complete the series: 21, 20, 18, 15, 11, ______?

Explanation

Step 1: Identify the pattern

Find the differences between consecutive terms:

  • 21 - 20 = 1
  • 20 - 18 = 2
  • 18 - 15 = 3
  • 15 - 11 = 4

The pattern of differences is: +1, +2, +3, +4

Step 2: Find the next difference

  • The next difference should be +5
  • 11 - 5 = 6