What is 10 x -38 mod 11?

What is 16 x -80 mod 16?

What is 278-421 mod 19?

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- Dec 3rd 2009, 07:06 AMsirellwoodvery quick modulo question
What is 10 x -38 mod 11?

What is 16 x -80 mod 16?

What is 278-421 mod 19? - Dec 3rd 2009, 07:47 AMBruno J.
$\displaystyle 10\times -38 \equiv -1 \times -38 \equiv 5 \mod 11$

$\displaystyle 16\times -80 \equiv 0 \times -80 \equiv 0 \mod 16$

$\displaystyle 278\times -421 \equiv 12 \times -3 \equiv 17 \mod 19$ - Dec 3rd 2009, 08:10 AMsirellwood
Thanks

Shouldnt i get numerical answers?

I got 9 for the 3rd one.... - Dec 3rd 2009, 02:34 PMBacterius
No it is indeed $\displaystyle 17$ for the last one, because $\displaystyle 278 \equiv 12 \ \ \ \ [19]$ and $\displaystyle -421 \equiv -3 \ \ \ \ [19]$.

EDIT : ah yes chiph588@ you are right, but why put a substraction question following two multiplication questions ? This is confusing (Nod) - Dec 3rd 2009, 03:52 PMchiph588@
For the third are you wanting $\displaystyle 278\cdot(-421) \mod{19} $ or $\displaystyle (278-421) \mod{19} $?

If it is the latter, then $\displaystyle 9 $ is the correct answer.