Question

SAT数学题

A simple square is any integer greater than 1 that has only three positive integer factors-----itself,its square root,and 1.Which of the following is a simple square?
A 121 B 100 C 81 D 64 E 33

Answer 1

求一个数这个数只能被它自己和它自己的平方根和1整除
A：121 is the product of only 11 and 11 , or 1 and 121. Since 11 is the square root of 121, then 121 has only three positive integer factors, itself 121 , its square root 11 , and 1
B: 100 is the product of 100 and 1, 20 and 5, 2 and 50, 4 and 25, etc. then 100 has more than 3 positive integer factor
c:81=9*9, 81*1, 3*27, where 3*27 is not itself nor its square root nor 1
d: 64=8*8, 2*32,where 2*32 is not itself not its square nor 1
e: 33=1*33, 3*11, and so it has only 2 positive integer factors.

then answer is A.

Answer 2

找一个数（simple square).此数特征：只有三个正因数：1，自己，还有自己的平方根
121:1, 11, 121
100： 1,2 ，5 ，10 ...........
81:1.，3， 9 ............
64:1， 2， 4..........
33:1,3,11..........
符合条件的只有A

Answer 3

A