divisible

[marianha]

. If x and y are integers, is xy + 1 divisible by 3?
(1) When x is divided by 3, the remainder is 1.
(2) When y is divided by 9, the remainder is 8.
my way:

x=3k+1
y=9k+8

(3k+1)(9k+8)+1=60k+9 therefore it is divisible by 3 (c)

is my way right? or is there any better way to solve such questions???

[12rk34]

For correct results it should be modified to
x=3k+1
y=9m+8
xy+1 = (3k+1)(9m+8)+1
= 27km+24k+9m+9 which is divisible by 3.
Although here the answer is the same, you should not use k in both the equations.

[marianha]

i got it thanks

[genius_in_the_gene]

let x = 3a+1
y= 9d+8

xy = 27ad+24a+9b+8.
xy+1 = 27ad+24a+9b+9

This is divisible by 3.
Hence C