A bank vault has three locks with a different key for each lock. Each key is owned by a different person. To open the door, at least two people must insert their keys into the assignated lock. The signals A, B and C are 1 if there is a key inserted into lock 1, 2 or 3 respectively. The equation for the variable Z which is 1 iff the door should open is:

Question 22 options:

	Z=AB + AC + BC
	Z=ABC
	Z=A + B + C
	None of the above

Question 23 (5 points)

A logic circuit realizing the function f has four inputs A, B, C and D. The three inputs A, B, C are the binary representation of the digits 0 through 7 with A being the most-significant bit. The input D is an odd-parity bit, ie the value of D is such that A, B, C and D allways contain an odd number of 1's. (For example, the digit 1 is represented by ABC = 001 and D = 0 and the digit 3 is represented by ABCD = 0111.) The function f has value 1 if the input digit is a prime number. (A number is prime if it divisible only by itself and 1; 2 is considered to be prime but 0 and 1 are not)

A list of the minterms and don't care minterms of f is :

Question 23 options:

	f = m(4,7,11,14) + d(0,3,5,6,9,10,12,15)
	f = m(2,3,5,7) + d(0,1,4,6,8,9,10,11,12,14,15)
	f = m(2,3,5,7,11,13) + d(0,1,2,4,6,8,9,10,12,14,15)
	None of the above

Hide hint for Question 23
Build the truth table for f(A,B,C,D) following the specifications given above. Observe that some of the rows of the truth table cannot hold realistic parameters and will never occurr and therefore should be assigned as don't care