单选题
The only contents of a parcel are 25 photographs and 30 negatives. What is the total weight, in ounces, of the parcel's contents?
(1)The weight of each photograph is 3 times the weight of each negative.
(2)The total weight of 1 of the photographs and 2 of the negatives is
(1)The weight of each photograph is 3 times the weight of each negative.
(2)The total weight of 1 of the photographs and 2 of the negatives is
【正确答案】
C
【答案解析】[解析] 设照片的重量为x盎斯，底片的重量为y盎斯，则由(1)可得：[*]，由(2)可得[*]。很明显单独根据(1)或单独根据(2)都不能解出x和y的值来，所以(1)和(2)单独都不充分；把(1)和(2)相结合可得一个两元一次方程组，从而可求出[*]包裹中的东西总重量为：[*]=7盎斯，所以(1)+(2)充分。