Assume you need a 64-to-1 multiplexer controlled by 6 select signals A through F, i.e., a binary number ABCDEF specifies the index of the input to be sent to the output. However, as we assume a logic gate can not have more than 8 inputs, such a MUX is not directly available. So you build this 64-to-1 MUX using 4-to-1 mux, such that minimum number of 4-to-1 mux are used. We build this 64-to-1 MUX using three levels of 4-to-1 MUXs where level 3 has one 4-to-1 mux and its output is the output of the original 64-to-1 mux.
The realization of this 64-to-1 mux using three levels of 4-to-1 muxes is such that Level i (i = 1,2,3) is controlled by select signals i.e. In level i, the most significant select line of each 4-to-1 mux is connected to and the least significant control line of each 4-to-1 mux is connected to .
To select input 27 i.e. (ABCDEF = 011011) and send it to the output, the value of should be