QUES 4. Ans C
If k and n are integers, is n divisible by 7?
1) n-3 = 2k
When n = 11, k = 4
11 - 3 = 2*4, n=11 is not divisible by 7
When n = 7, k = 2
7 - 3 = 2*2, n=7 is divisible by 7
Cannot say for sure. INSUFF
2) 2k-4 is divisble by 7.
Does not say anything about n. INSUFF
From 1) and 2)
n-3 = 2k
n-3-4 = 2k -4
n-7 = 2k-4 => n-7 is divisible by 7 => n is divisible by 7. SUFF, so C.
QUES 7. Ans B
If x+y+z > 0, is z > 1?
1) z > x+y+1
Try z = 0.75, x = y = - 0.25. Here z
Try z = 2, x = y = - 0.25. Here z > 1
So INSUFF
2) x+y+1 0 > x+y+1
Also x+y+z > 0
x+y+z > x+y+1 => z > 1 SUFF
QUES 9. Ans A ??
If x and y are integers between 10 and 99, inclusive, is (x-y)/9 is an integer?
1) x and y have the same two digits, but in reverse order. SUFF
This is actually a well discussed condition for division by 9, as far as I know.
2) The tens' digit of x is 2 more than the units' digit, and the tens' digit of y is 2 less than the units' digit.
I started to working on this one, and it seemed to lead nowhere. I am not 100% sure if this is INSUFF or not. Maybe someone else can chime in?