MahmoudFawzy
from the given,
if a= 1, then b = any integer from -9 to 9 except 0
if a = -1, then b = any even integer from -8 to 8 except 0
from statement (1),
if a =1, then b = 1 or -1
if a = -1, then b = any integer from -9 to 9 except 0 --> insufficient
from statement (2),
if a =1, then b = 1,5,6 (mono-cyclic integers) or -5 ( which leads to a mono-cyclic integer 5)
if a =-1, then b = 5 or -5 (which lead to a number with 5 as its unit digit) --> insufficient
upon combining,
if a = 1, then b = 1 --> sufficient C
if a = -1, then b has no valid common value (which means that a is not equal -1)
For statement (2), you almost have it right:
if
a = 1 then
b =
1,5,6 AND -4,-5,-9 since negative single digits are allowed
if
a = -1 then
b =
9,5,4 AND -1,-5,-6 since negative single digits are allowed
combining 1+2:
if
a = 1, then
b = 1 if
a = -1, then
b = -6 or 4 So now you have two choices for a itself, where b can be 1, -6 or 4
Insufficient