问两道数学题，归纳规律

1.       If M and N are positive integers that have remainders of 1 and 3, respectively, when divided by 6, which of the following could NOT be a possible value of M+N?

A.      86

B.      52

C.      34

D.     28

E.      10

答案是C 请NN解释一下。而且我对这类余数的题不太熟，有没有什么规律？

2.       A family made a down payment of $75 and borrowed the balance on a set of encyclopedias that cost $400. Then balance with interest was paid in 23 monthly payments of $16 each and a final payment of $9. The amount of interest paid was what percent of the amount borrowed?

A.      12%

B.      6%

C.      14%

D.     16%

E.      20%

答案是D 利息该怎么算？

谢谢大家！

1.       If M and N are positive integers that have remainders of 1 and 3, respectively, when divided by 6, which of the following could NOT be a possible value of M+N?

A.      86

B.      52

C.      34

D.     28

E.      10

我的想法是：设M=6*m+1, N=6*n+3,则M+N=6*（m+n)+4,那么答案应该选A，因为只有86-4=82不能被6整除

2.       A family made a down payment of $75 and borrowed the balance on a set of encyclopedias that cost $400. Then balance with interest was paid in 23 monthly payments of $16 each and a final payment of $9. The amount of interest paid was what percent of the amount borrowed?

A.      12%

B.      6%

C.      14%

D.     16%

E.      20%

（1）先计算共付了多少钱：23*16+9=377

（2）计算共借了多少钱：400-75=325

（3）利息=377-325=52

  （4）利息占所借金额的比例=52/325=16%

Q1.参照楼上mm的解法

Q2.这个题目要先把贷款分离出来,400-75=325

之后一共支付23*16+9=377

(377-325)/325= 0.16