Is the sum of integers a and b divisible by 7?
(1) a is not divisible by 7.
(2) a - b is divisible by 7.
(1) a is not divisible by 7.
(2) a - b is divisible by 7.
The Ans is C
for a=15 and b=1 a+b=16 not divisible by 7(1) a is not divisible by 7.
for a=15 and b=-1 a+b=14 divisible by 7
not suff
for a=21 and b=7 a-b is divisible by 7 and a+b=14 divisible by 7(2) a - b is divisible by 7.
for a=15 and b=1 a-b is divisible by 7 but a+b=16 is not divisible by 7
not suff
combining the (1) and (2)
for a=15 and b=1 a-b is divisible by 7 but a+b=16 is not divisible by 7
for a=20 and b=-1 a-b is divisible by 7 but a+b=16 is not divisible by 7
Suff
Hope it helps
