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The sum of the series 2· 20 C 0 + 5· 20 C 1 + 8· 20 C 2 + 11· 20 C 3 + …. + 62· 20 C 20 is equal to -

1. 2 23
2. 2 25
3. 2 26
4. 2 24

Correct answer: 2 25

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