`-` is a binary operation on

Which of the following is true? * defined by (a) a*b=(a+b)/2 is a binary operation on Z (b) * defined by a*b=(a+b)/2 is a binary operation on Q (c) all binary commutative operations are associative (d) subtraction is a binary operation on N

Which of the following is true? * defined by a*b=(a+b)/2 is a binary operation on Z (b) * defined by a*b=(a+b)/2 is a binary operation on Q (c) all binary commutative operations are associative (d) subtraction is a binary operation on N

+ is not a binary operation on

Which of the following is not a binary operation on R?

The operation ** defined by a ** b =(ab)/7 is not a binary operation on

A binary operation is chosen at random from the set of all binary operations on a set A containing n elements.The probability that the binary operation is commutative,is

A binary operation is chosen at random from the set of all binary operations on a set A containing n elements. The probability that the binary operation is commutative, is