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Let A = {1,2,3,.......,10} and B = ⎭ ⎬ ⎫ ⎩ ⎨ ⎧ = < ∈ 1 ) n , m ( gcd and n m , A n , m : n m Then n(B) is equal to :

1. 31
2. 36
3. 37
4. 29

Correct answer: 31

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