12 X 21/2 =

1st way: 12 x 21 = 252/2 = 126

Or 2nd way: 21/2 = 10.5 x 12 = 126

126. Think of problems like these as 12/1 times 21/2. 12 times 21 would be 252 and 1 times 2 would be two. This would leave you with 252/2. When simplified, 252/2 is 126.