I'm doing some reading about CMOS circuits and the likes. In the book I'm using it tells me to derive the simplest sum of products for an expression from a truth table. The canonical sum of product is as follows: *- AND !- NOT + - OR (!x1*!x2* !x3*!x4) + ( !x1*x2*!x3*!x4) +(x1*!x2*!x3*!x4) = f Using Boolean algebra I was able to simplify to (!x2*!x3*!x4) + (!x1*!x3*!x4)= f which is the simplest sum of products. Then the book then asks how many transistors are needed to implement the sum of products circuit using CMOS AND,OR,and NOT gates. My solution was as follows: We need : 2 -3input CMOS AND gates => 2(4*2) transistors = 16 transistors 4- CMOS inverters => (4*2) transistors = 8 transistors 1- 2 input CMOS OR gate => 1(3*2) transistors =6 transistors 16+8+6 = 30 transistors But the answer is 28 transistors i'm not sure what I'm doing wrong. I realize that 8 transistors are used to implement CMOS 3input AND gate, 2 transistors are needed for CMOS 1input inverter and 6 transistors for 2input OR gate. What I'm I doing wrong ?