help what 141 substract etc

Question

Find the cardinal number for the following sets.

A = {104 , 105, 106 , 107 ,..., 141}
     
B = {104 , 106 , 108 , ..., 304 }

Answer 1

for A, just subtract 103 from 141 to get the # of elements in the set.

 

for B, subtract 102 from 304, AND THEN DIVIDE BY TWO.  Do you see why?