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Find the cardinal number for the following sets.

A  = {104 , 105, 106 , 107 ,..., 141}

B  = {104 , 106 , 108 , ..., 304 }

Set A = {  104 , 105, 106 , 107 ,..., 141 }
subtract from each element 101 we have 1, 2, 3, ... , 40
n(A) = 141-101 = 40

Set B = {  104 , 106 , 108 , ..., 304  }
subtract from each element 102 we have 2, 4, 6, ... , 202
202 = 2n

so

n(B) = 202/2 = 101