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by maihuna » Tue Mar 15, 2011 12:15 pm
If a and b are positive integers and a > b, what is the remainder
when a2 -2ab + b2 is divided by 9 ?
(1) The remainder when a - b is divided by 3 is 2.
(2) The remainder when a - b is divided by 9 is 2.
Charged up again to beat the beast :)
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Source: — Data Sufficiency |
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by clock60 » Tue Mar 15, 2011 12:50 pm
here got B
what is remaider if
(a-b)^2 is divided by 9

(1) a-b=3m+2
(3m+2)^2=9m^2+12m+4,
9m^2 divisible by 9, remaider when (12m+4) is diveded by 9 is not fixed.
say m=1 then 12+4=16=9*1+7 remaider 7
m=2, 24+4=28=3*9+1 remaider 1 so insuff

(2) a-b=9k+2
(9k+2)^2=81k^2+36k+4, remaider is 4 fixed here
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by force5 » Tue Mar 15, 2011 2:40 pm
correct answer it shld be B
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