Q10:

What is the value of (x - y)⁴?

(1) The product of x and y is 7.

(2) x and y are integers.

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

D. EACH statement ALONE is sufficient.

E. Statements (1) and (2) TOGETHER are NOT sufficient.

答案是c，百思不得其解……题目中的是减号还是乘号，偶笨笨……

so we want to know the value of (x - y)^4,

1) the product of x and y is 7, since this doesn't tell much except x * y = 7, and since x and y could be non-integers(ie: if x = 3.5 and y = 2, then the answer is different from when x = 7 and y = 1), we don't know the answer, thus 1) by itself is not sufficient

2) x and y are integers, by simply knowing that x and y are integers, we can not conclude what the value of (x - y)^4 is, for x and y could be any integer, thus 2) by itself is not sufficient

1) and 2) together, now we know that x * y = 7 and x and y are integers, thus, x and y could only be either (7, 1), (1, 7), (-7, -1), (-1, -7), and when x and y are any of the above pair, the value of (x - y)^4 = 6^4, thus, 1) and 2) together are sufficient, thus the answer is C