acutetrader Posted September 12, 2005 Share Posted September 12, 2005 What is the remainder when 7^625 is divided by 15? Try it first, Pls Provide your brief calculation , I'll post the OA later :) Quote Link to comment Share on other sites More sharing options...
charu_mulye Posted September 12, 2005 Share Posted September 12, 2005 My method for solving this type of question wd be : 7^0 mod 15 = 1 7^1 mod 15 = 7 7^2 mod 15 = 4 7^3 mod 15 = 13 7^4 mod 15 = 1 ... now the cycle repeats since the cycle is of length 4, we have 7^4n mod 15 = 1 n=0,1,2.. 7^(4n+ 1) mod 15 = 7 Thus 7^625 = 7^ (4* 156) +1 = 7 Remainder is 7 Quote Link to comment Share on other sites More sharing options...
jsr_idhar Posted September 12, 2005 Share Posted September 12, 2005 What are the options. Quote Link to comment Share on other sites More sharing options...
CTG1983 Posted September 12, 2005 Share Posted September 12, 2005 Charu, can u plz explain ur process a bit further. looks interesting. Quote Link to comment Share on other sites More sharing options...
tictaktoe Posted September 12, 2005 Share Posted September 12, 2005 agree with the solution. whn n=0 r=1 (also true for 0+4=4, 4+4=8, 12, 16, etc OR ANY MULTIPLE OF 4) n=1 r = 7 ( also true for 1+4=5, 5+4=9, .13, etc or (any multiple of 4 )+ 1 n=2 r = 3 ( true for any mutliple of 4)+2 n=3 r = 13 625 = 4*156 + 1 .. corresponds to second, so r = 7 Quote Link to comment Share on other sites More sharing options...
acutetrader Posted September 13, 2005 Author Share Posted September 13, 2005 OA is 7 , thanks Quote Link to comment Share on other sites More sharing options...
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