gmatophobia
PS Question 1 - Nov 20 For an integer n, the function f(n) is defined as the product of all integers from 1 to n, where n is greater than 10. Which of the following is NOT a factor of f(n)+1?
I. 2
II. 3
III. 10
A. None
B. II only
C. I and II only
D. I and III only
E. I, II and III
Source:
Expert’s Global | Difficulty: Hard
Tricky question. Can be much harder if you don’t see the logic.
Remember that x and x+1 have no common factors.
Therefore, for any value of n>10 in the function f(n). It will have as a factor all the previous numbers.
Take the case of n=11. f(n) will be 11!, which has all integers from 1 to 11 as factors.
because n is always greater than 10, 2,3 and 10 itself are included in n!, and therefore n!+1 cannot contain any number from n! as a factor. So E.