NN看下这两道PS的题

xihongshi7_7

1.If n is an integer, which of the following CANNOT be a factor of 3n+4?
A 4 B 5 C 6 D 7 E 8 我觉得没有答案

2.In Township K, 1/5 of the housing units are equipped with cable television. If 1/10 of the housing units, including 1/3 of those that are equipped with cable television, are equipped with videocassette recorders, what fraction of the housing units have neither cable television nor videocassette recorders?
A 23/30 B 11/15 C 7/10 D 1/6 E 2/15
答案给的是A，我怎么说都是B啊，是不是答案给错了？

happyapt2006

1，

i think the answer is C

because if n is odd, it can be described in '3(n-1)+7', then '6(n-1)/2+7'. note: n-1 is even so (n-1)/2 is an interger....

2 i agree with you. but most of time, the answers are not wrong. i hope someone can give the right way

mbamom

2 the answer is 23/30

1-(1/5+1/10-1/5*1/3)=23/30

you might misunderstand this part "including 1/3 of those that are equipped with cable television" as "of which1/3 are equipped with cable tv"

happyapt2006

pretty good! thank you very much!