If y>0, is y^3-y divisible by 4?
(1) y^2+y is divisible by 10 --> if y=10 then y(y-1)(y+1)=10*9*11, so not divisible by 4 (product of 2 odd and not multiple of 4 will not be divisible by 4) BUT if y=100 then y(y-1)(y+1)=100*99*101, so divisible by 4 (100 is a multiple of 4, hence product will be divisible by 4). Sufficient.
(2) For a certain integer k, y=2k+1 --> y=odd --> y-1=even and y+1=even --> y(y-1)(y+1) is a multiple of 4 (product of 2 even numbers is a multiple of 4, OR as y-1 and y-1 are consecutive even numbers, thus one of them must be multiple of 4). Sufficient.
Pleas use "^" for powers, and formating for formulas.
answer is definitely B , as the product of 2 consecutive even numbers is divisible by 4.
There is a small typo above , it should be (y-1) and (y+1) are 2 consecutive even numbers and not
(y-1 ) and ( y-1) are 2 consecutive even numbers ,
Hope this prevents any confusion.