GWD 17-21

[enim]

Q21.
Harvey teaches a certain number of biology students in 2 classes, K and L. He can divide the students in class K into 7 groups of n students each. He can divide the students in class L into 6 groups of p students each with 1 student left over. How many students are in class L?

(1)n=p
(2)There are 5 more students in class K than in class L.

Ans:C

I chose B

條件一 一定不充分
條件二
我的公式是K=L
K=7n+1
L=6p+1
→7n+1=(6p+1)+5
→7n-6p=5
7和6是互質，所以n和p一定為5，7n-6p=5這個等式成立

不知道我哪裡錯了？
可以請版上大大指點一下
謝謝

[stwang]

依題意 式子應該如下所列:
K=7n
L=6p+1

(2)7n=(6p+1)+5
7n=6p+6
n=6 p=6
n=12 p=13
所以(2)不充分

如果加條件(1)n=p
7n=6n+6 n=6
可以算出學生有37人
所以答案為(C)

有錯請指正唷....

[enim]

thank you stwang大大

我竟然眼花了而且打題目的時候，完全沒發現

[jerry7271]

He can divide the students in class L into 6 groups of p students each with 1 student left over

請問L的這個公式我怎麼看都是
L=6P-1 怎麼是 L=6P+1 呢？
怎麼看的啊...

[scujean]

He can divide the students in class L into 6 groups of p students each with 1 student left over

請問L的這個公式我怎麼看都是
L=6P-1 怎麼是 L=6P+1 呢？
怎麼看的啊...

它把學生分成6組，每組P人，最後還有1人落單