GWD2-Q2&Q7

[Ally]

Q2:
If n is a positive integer and the product of all the integers from 1 to n, inclusive, is divisible by 990, what is the least possible value of n?
A.8
B.9
C.10
D.11
E.12 Answer:D



Q7:Last year, 36 houses in a certain development had roof repairs and 48 houses were repainted. If 20 houses in the development had roof repairs but were not repainted last year, how many houses were repainted but did not have roof repairs?

A. 12
B. 16
C. 20
D. 28
E. 32
Answer E

Help: 真不知道該怎麼算 有沒有可以敎敎我 ? :-$

[huacy]

請將提目分開不同文貼 這樣版主比較好整理 也方便其它人閱讀

Q2.
n! 要被 990 整除 一定需要 11 的倍數
所以選項中最小的可能 n 為 11

Q7.
已修的房子有36間
已漆的房子有48間
已修未漆的房子有20間

所以 36 - 20 = 16 等於已修已漆的房子數
再將 已漆的房子減去已漆已修的房子 就等於已漆未修的房子數
所以 48 - 16 = 32

[Ally]

[quote="huacy"][color=red]請將提目分開不同文貼 這樣版主比較好整理 也方便其它人閱讀[/color]

Ally: 了解 謝謝你!

Q2.
n! 要被 990 整除 一定需要 11 的倍數
所以選項中最小的可能 n 為 11

Q7.
已修的房子有36間
已漆的房子有48間
已修未漆的房子有20間

所以 36 - 20 = 16 等於已修已漆的房子數
再將 已漆的房子減去已漆已修的房子 就等於已漆未修的房子數
所以 48 - 16 = 32[/quote]