逻辑问题求教,96-OCT

chinesecheese

24. Each December 31 in Country Q, a tally is made of

the country's total available coal supplies-that is,

the toal amount of coal that has been mined

throughout the country but not consumed.  In 1991

that amount was considerably lower than it has been

in 1990.  Furthermore, Country Q has not imported or

exported coal since 1970.



If the statements above are true, which one of the

following must also be true on the basis of them?



(A) In country Q, more coal was mined in 1990 than

      was mined in 1991.

(B) In country Q, the amount of coal consumed in

     1991 was greater than the amount of coal

      mined in 1991.

(C) In Country Q, the amount of coal consumed in

      1990 was greater than the amount of coal

      consumed in 1991

(D) In country Q, the amount of coal consumed in

      1991 was greater than the amount of coal

      consumed in 1990

(E) In Country Q, more coal was consumed during

      the first half of 1991 than was consumed

      during the first half of 1990.





答案是B





我的理解, 每年的tally=coal mined - coal consumed的差别, 条件只说明91年的差别比90年的小,

不懂为十么答案一定是B? 谢过

jeremyang

suppose 1990's tally is X



1991's amount of mined is A, amount of consumed is B ,so 1991's tally is Y=(A-B)+X



and Y<X so we get (A-B)<0



mined is less than consumed is Answer B

chinesecheese

你的意思是说tally是每年cumulate的数字, 是吧?  我原来以为说的是每年的tally是independent的, 按你说的, 就明白了.谢谢.

lifechaser

why 1991's tally is added by X?