Question

GMAT两道数学题

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.

If the units digit of the three-digit positive integer k is nonzero, what is the tens digit of k?
(1) The tens digit of k + 9 is 3.
(2) The tens digit of k + 4 is 2.
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.

第一题答案是C，第二题答案是A，要详细步骤哦！谢谢了！！！！！！！！！！
第一题是（X-Y)的4次方的意思

Answer 1

第一题，只有(1),算上小数, x和y的变数太多 NOT sufficient

只有(2),x和y的变数还要多 NOT sufficient
(1)+(2),得出x=1,y=7或x=7,y=1或x= -1,y= -7或x= -7,y= -1四种情况,
4种情况下|x-y|均等于6, (x - y)^4=6^4 ,故sufficient，选C

第二题，一个三位数的个位数不是0，问十位数是多少
只有(1), k+9, k的个位数+9必定要进位, 所以k的十位数为3-1=2, sufficient
只有(2), k+4, k的个位数+4可能进位可能不进位, 所以k的十位数无法确定，
可能是2或1, NOTsufficient
故选A