If w, y, and z are positive integers, and w = y – z, is w a perfect square?
(1) y + z is a perfect square.
(2) z is even
first of all. perfect squares: 0, 1, 4, 9, 16....0 is a positive even integer
assume y=4 and z=0 then yes w=4 perf. sq.
assume y=12 and z=4 then no w=8 is not a perf. sq.
z is even. there is no info about y and it can be anything
refer to the 1st statement again not suff.
combined. not suff.