Joe argued that if every employee received an $3000 increase in their yearly salary then the mean employee salary would also increase by $3000. If this were not true then one counter-example would prove it is not true BUT if it was true then no number of counter-examples would prove it was true. They would only suggest that it is true. Therefore given(see image below)

A= (a, ap, a3, . . . . an-1, an) and B= (a+k, a, +k, a; +k. .... ajj+ k, an+ k) prove that b = atk