Hi,
Question: Remainder when y^2 divided by 6 ?
Any integer when divided by 6 leaves remainders as 0,1,2,3,4 and 5.
Statement I is sufficient:
Prime number greater than 10.
Yes there is a rule which says, when any prime number greater than 3 can be expressed as 6n+1 or 6n+5.
So according to the rule,
y=6n+1 or y = 6n+5
y^2 = 36n + 12n + 1
or
y^2 = 36n + 60n + 25.
So, both expression when divided by 6, leaves the remainder 1.
Even if you don’t remember this rule(this rule has been discussed in Official GMAT guide), its okay, you just need to try out some values and check out the pattern of y^2. Different pattern then
its not sufficient, if it gives you same result every time then it is sufficient.
Let’s say,
y = 11 , 13, 17, 19
y^2 = 121, 169, 289, 361.
All leaves remainder 1 when divided by 6(Divisibility rule for 6 is it should be divisible by both 3 and 2). So sufficient.
Statement II is sufficient:
y = 1, 5, 7, 11, 13, 17,..
y^2 = 1, 25, 49, 121, 169, 289..
Again, all leaves remainder 1 when divided by 6.
So, each alone are sufficient. So answer is D.
Trying out numbers would be the ideal approach for these types of questions.
Hope this helps.