Is the units digit of integer x2−y2 a zero?
(1) x−y is an integer divisible by 30
(2) x+y is an integer divisible by 70
(1) x−y is an integer divisible by 30
(2) x+y is an integer divisible by 70
(x+y)(x-y) --> INT-->doesnt means x & y are INT
Statement 1:
(x-y)/30
Suppose x-y = 60 --> x = 61.2 & y = 1.2
So, (x+y)(x-y) = 62.4 * 60 ==> _ _ 4 NO
Suppose x-y = 60 --> x = 61 & y = 1
so, (x+y)(x-y) = 62*60 ==> _ _ 0 YES
INSUFFICIENT
Statement 2:
(x+y)/70
Suppose x + y = 70 --> x = 71.2 & y = 1.2
So, (x+y)(x-y) = 72.4 * 70 ==> _ _ 4 NO
Suppose x + y = 70 --> x = 71 & y = 1
so, (x+y)(x-y) = 72*60 ==> _ _ 0 YES
INSUFFICIENT
Combining...
both (x-Y) & (x+y) has "0" as unit digit
SUFFICIENT
Answer [spoiler]{C}[/spoiler]
