[求助] 2个OG 12数学题

qinxia823

a marketing firm determined that,of 200 households surveyed, 80 used neither Brand A nor Brand B soap,60 used only Brand A soap,and for every household that used both brands of soap,3 used only Brand B soap. How many of the 200 households surveyed both brands of soap?

A15   B20    C30    D40   E45

the sum of prime numbers that are great then 60 but less then 70 is

A67  B128  C191  D197   E260

OG有讲解的，但是没有看明白，有知情的说说，谢谢！

korea_univ

选A 设两个brand都用的人有m个，那么60+m+3m+80=200 求m

选B 61+67=128

qinxia823

以下是引用korea_univ在2009/8/5 16:18:00的发言：

选A 设两个brand都用的人有m个，那么60+m+3m+80=200 求m

选B 61+67=128

悟出来了，谢谢！