In the country of Veltria, the past two years' broad economic recession has included a business downturn in the clothing trade, where sales are down by about 7 percent as compared to two years ago. Clothing wholesalers have found, however, that the proportion of credit extended to retailers that was paid off on time fell sharply in the first year of the recession but returned to its prerecession level in the second year. Which of the following, if true, most helps to explain the change between the first and the second year of the recession in the proportion of credit not paid off on time? (A) The total amount of credit extended to retailers by clothing wholesalers increased between the first year of the recession and the second year. (B) Between the first and second years of the recession, clothing retailers in Veltria saw many of their costs, rent and utilities in particular, increase. (C) Of the considerable number of clothing retailers in Veltria who were having financial difficulties before the start of the recession, virtually all were forced to go out of business during its first year. (D) Clothing retailers in Veltria attempted to stimulate sales in the second year of the recession by discounting merchandise. (E) Relatively recession-proof segments of the clothing trade, such as work clothes, did not suffer any decrease in sales during the first year of the recession. 这道题错选了A。 思路如下： 题目问的是为什么在经济不好，衣服卖不动的情况下，第一年零售商还不上钱第二年就能还上了。讲的是零售商还钱的问题。 当时留下的是A,C,D 排除D是因为觉得，即使刺激销售量衣服打折也不能说明能还上钱。可能打折卖1块，纵使家当全卖了也不够。 排除C是因为觉得， 那些本身经济状况就很差的在第一年被淘汰掉以后，剩下的那些没说经济状况如何啊，如果也不咋地，第二年还是得淘汰啊。 A选项当时觉得，即使credit extended，对pay off on time也无太大用处，但最起码跟原文意思接近。所以选了A。

GMAT数学（博智教材）第62页：If X is equal to the sum of the even integers from 40 to 60, inclusive, and y is the number of even integers from 40 to 60, inclusive, what is the value of x+y? X=40+42+44......60=550 Y=(60-40)/2+1=11, 答案应该是561，为什么书后面的答案显示是560？

数学书61页36题，一个男的卖每条7块的领带和每件14元的衬衫。如果他总共卖了10件，110元，求卖了几条领带？ 我得小数，选项里没有。

DS：5个数中 median 小于 average ；另外7个数也median 小于 average，然后这12个数没有重复的，12个数放在一个数集里面，问是不是median 小于average？ 条件1：7个的average 小于 5个的average 条件2：7个的median 小于 5个的 median

DS：一个三位数xyz是9的倍数，问x+y+z=9？ 条件1：x+y+z<15 条件2：x+y+z>8

question

这种ds题目里面有比例关系的我特别弱，老师能帮我梳理一下这种题拿到药怎么入手吗

老师这个题目帮我讲解一下，机经答案我看了还是不明白。

这个题目机经写的特别复杂，老师能帮我讲一下吗

老师，能帮我梳理一下这个题目吗

题目：of the 200 students at college T majoring in one or more of the sciences, 130 are majoring in chemistry and 150 majoring in biology. If at least 30 of the students are not majoring in either chemistry or biology, then the number students majoring in both biology and chemistry could be any number from a) 20 to 50 b) 40 to 70 c) 50 to 130 d) 110 to 130 e) 110 to 150 问题：这道题能理解到是用集合的知识点，但是无论怎么做都无法突破，得到最后结果。还请老师讲解。谢谢