PP-T2-DS200

[emmaaqua]

200.If d is a positive integer and f is the product of the first 30 positive integers, what is the value of d ?

(1) 10d is a factor of f.
(2) d > 6

正解為C


謝謝~!!

[ipas3]

難怪沒有人回, 我來修正一下題目
200.If d is a positive integer and f is the product of the first 30 positive integers, what is the value of d ?
(1) 10^d is a factor of f.
(2) d > 6

由題意, f=30!
(1) 30!/(10^d)要可以整除, 10^d=2^d*5^d, 就看30!有幾個2和5的因數 (這邊看5就好因為2一定比5多)
5, 10, 15, 20, 25, 30, 共七個 (25要算兩個).
so d=1,2,3,4,5,6,7 insufficient

(2)d>6
so d=7

答案(C)