For museum X, the total entrance fee is $x plus $z each person older than 30. For museum Y, the total entrance fee is $y plus $w each person older than 40. When 50 people enter museums X and Y, is the total entrance fee of the museum X smaller than that of the museum Y?
1) x<y
2) z<w
==> In the original condition, there are 6 variables (M
x, x, z, My, y, w) and 2 equations (M
x=x+20z and M
y=y+10w) and in order to match the number of variables to the number of equations, there must be 4 more equations. Since there is 1 for con 1) and 1 for con 2), E is most likely to be the answer. By solving con 1) and con 2), if (x,z,y,w)=(1,1,2,2), from M
x=21 M
y=22, it is yes, but if (x,z,y,w)=(2,2,3,3), from M
x=42 M
y=33, it is no, hence it is not sufficient.
Therefore, the answer is E.
Answer: E