两道PREP2的题，帮忙解答一下，谢谢

huangxiuying

123.   12975-!-item-!-187;#058&009772

When positive integer n is divided by 3, the remainder is 2; and when positive integer t is divided by 5, the remainder is 3.  What is the remainder when the product nt is divided by 15 ?（C）

(1) n - 2 is divisible by 5.

(2) t is divisible by 3.

我选E

112.   11750-!-item-!-187;#058&008431

For a certain race, 3 teams were allowed to enter 3 members each.  A team earned 6 - n points whenever one of its members finished in nth place, where 1 <= n <= 5.  There were no ties, disqualifications, or withdrawals.  If no team earned more than 6 points, what is the least possible score a team could have earned?（D）

(A) 0

(B) 1

(C) 2

(D) 3

(E) 4

题目看的不太懂，能解释一下吗？谢谢

jh1904

123. Set n=3a+2, t=5b+3,

(1) n-2 is divisible by 5, 3a is divisible by 5, set n=15c+2

(2) t is divisible by 3, 5b+3 is divisible by 3, 5b is divisible by 3, set t=15d+3

nt/15, remainder =6.

112. 1+2+3+4+5, totally 15 points to be won by 3 teams. No team has won more than 6 points. If two teams have won exactly 6 points, the other team would have won 3 points. If one of the 3 teams won only 1 or 2 points, one of the other 2 teams would have won more than 6 points. So, the answer is 3.

huangxiuying

LS实在是大大好人，谢谢