Question

If $5x\equiv 2\left(mod7\right),$ then which of the following holds true?

• A. $x\equiv 6\left(mod9\right)$
• B. $x\equiv 6\left(mod7\right)$
• C. $x\equiv 7\left(mod6\right)$
• D. $x\equiv 2\left(mod7\right)$

Answer 1

Answer: (B)

$x\equiv 6\left(mod7\right)$

$5x\equiv 2\left(mod7\right)\equiv -5\left(mod7\right)$
$\Rightarrow x\equiv -\left(mod7\right)\equiv 6\left(mod7\right)$
Ans: B