Is quadrilateral MNOP a square?
(1) MN = NO = OP
(2) Angle N and angle O are right angles
Stupid, annoying question (sorry, I just had to vent):
1) tells us the lengths of three sides but this theoretically still could leave us with a fourth side that is longer/shorter than the rest, so insufficient
2) Tells us that our quadrilateral is either a rectangle or a square, insufficient.
1 + 2 tell us that our quadrilateral is a square, because 2) restricts the possible shapes that 1) can take, and combining the two tells us how long the fourth side in 1) is, so sufficient.