请教CXD 3道数学题目

helenli8

1.if n is a positive integer and n square is divisiable by 72, then the largest positive integer that must divide n is

a.6         b.12          c.24           d.36          e.48

answer is C

2. a survey of  100 persons revealed that 72 of them had eaten at restaurant P and that 52 of them had eaten at restaurant Q. Which of the following could not be the number of persons in the surveyed group who had eaten at both P and Q?

a. 20        b.24            c.30            d.50              e.52

answer is A

3.$2000 is deposited into a savings account that earns interest at the rate of 10% per year, compounded semiannually. How much money will there be in the account at the end of one year?

a. 2105        b.2200          c 2205             d.2400              e.2600

answer is C

算了好久还是不行,请教各位帮忙,谢谢

helenli8

SORRY,第一道 ANSWER IS B

deyu578

3. First,at the end of six months,the interest earned is: 2000*10%/2=100

Second,at the end of the year,the interest earned is: 2100*10%/2=105

So the answer is: 2000+105+100=2205

helenli8

谢谢DEYU,第一/二题能帮忙解释下吗?

joannsy

第一题
n^2----72=2^3×3^2说明
n最小则 有---2^3  与  3^2  中的取得最小数是 1.5 和1（1 我们可以完全放心的说N里最少可以有一个3；而1.5非整数，所以2是其最小整数）
则n最小可能是2^2×3^1 =12

也可以排除：

求N的最大的除数，那么我们必须保证n中n有一个3（因为我们没有办法保证n是否可能有2个）因此排除d.36   e.48
n中2最大能确保是2，排除c.24

则：a b 选项中取最大就是12

所以选择b

helenli8

谢谢JOANNSY详细解答.你好牛哦,好多数学题对我来说都好难.谢谢你帮我开窍,呵呵

第二题,可以请哪位帮帮,好吗?