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divisiblity problems

Expert replies
Source: — Data Sufficiency |

by praky_rules » Sat Sep 19, 2009 10:25 am
St 1) => Choose x=4 (divided by 3 , remainder = 1) and y=2, then xy + 1 = 9 ...divisible by 3.
Choose x=4 (divided by 3 , remainder = 1) and y=1, then xy + 1 = 5 ...not divisible by 3.
INSUFF
St 2) Similarly....B is also Insuff

Together
assume x = 3k+1
y=9m+8
=> xy+1 = 27km+24+9m+9 - Divisible.


So C
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