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The value of ( 21 C 1 – 10 C 1 ) + ( 21 C 2 – 10 C 2 ) + ( 21 C 3 – 10 C 3 ) + ( 21 C 4 – 10 C 4 ) + ... + ( 21 C 10 – 10 C 10 ) is

1. 2 21 – 2 10
2. 2 20 – 2 9
3. 2 20 – 2 10
4. 2 21 – 2 11

Correct answer: 2 20 – 2 10

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