[問題] GWD4-Q29

[kwtluck]

Q29:
The annual rent collected by a corporation from a certain building was x percent more in 1998 than in 1997 and y percent less in 1999 than in 1998. Was the annual rent collected by the corporation from the building more in 1999 than in 1997?
(1)x > y
(2)(XY)/100 < x–y
Answer:B

麻煩各位大大解題 Thanks!!~~

[spreewell]

1997's rent=1998's rent*1/(1+x/100)
1999's rent=1998's rent*(1-y/100)
if the rent was more in 1999 than in 1997,that means
1/(1+x/100) < (1-y/100) →
1 < (1-y/100)(1+x/100) →
1 < 1+x/100-y/100-xy/10000 →
xy/10000 < x-y/100 →
xy/100< x-y
so correct answer is B

[kwtluck]

原來這題要"倒退推"~了解
**再次感謝spreewell大大詳盡的解說**