25. A total of 774 doctorates in mathematics were granted to United States citizens by American universities in the 1972-1973 school year, and W of these doctorates were granted to women. The total of such doctorates in the 1986-1987 school year was 362, and w of these were granted to women. If the number of doctorates in mathematics granted to female citizens of the United States by American universities decreased from the 1972-1973 school year to the 1986-1987 school year, was the decrease less than 10 percent?
(1)1/10< W/774 < 1/9
(2)W=w+5
Ans; C
请教解题思路
另外，less than 10 percent?是什么的percent
是否：W/774- w/362 是否等于10percent?
percent exchange
Often a problem will ask for the percent increase or decrease from on quantity to another , eg, if the price of an item increases from $24 to $30 what is the percent increase in price ? To find the percent increase , first find the amount of the increase then divide this increase by the original amount , and expreess this quotient as a percent In the eg , the percnet increase is 30-24 therefore the percent increase is 6/24=25%
Likewise , to find the percent decrease eg the price of an item is reduced from $30 to $24 first find the amount of the decrease then divide this decrease by the original amount , and expreess this quotient as a percent 6/30=20%
分子是the number decreased from the 1972-1973 school year to the 1986-1987 school year;分母是from the 1972-1973 school year ，对吗？
另外，我找OG MATH REVIEW P37找不到相关解释。
再举下一题为例：
13. Did the population of Country S increase by less than 20 percent from 1965 to 1975 ?
(1) The population of Country S in 1965 was 180 million.
(2) The population of Country S in 1975 was 1.17 times what it was in 1965.
Ａns: B
(2) set the population of Coutry S in 1975 as X, set the population of Country S in 1965 as Y
idea shall be as follow:
(X-Y)/X
and (2)=> X=1.17Y 代入，得出结论
因此分母应是两个概念（１９６５， １９７５）中的前一个对吗？
