Model Paper 5 — Applied Maths STD 12 Science — Question
CBSE BoardEnglish MediumSTD 12 ScienceApplied MathsModel Paper 52 Marks
Question
Solve: $12 x \equiv 44(\bmod 59)$
✓
Answer
We know that $a \equiv b (\bmod m ) \Rightarrow \frac{a}{x} \equiv \frac{b}{x}\left(\bmod \frac{m}{d}\right)$, where $d =( x , m )$. $ \begin{array}{l} \therefore 12 x \equiv 44(\bmod 59) \\ \Rightarrow 3 x \equiv 11(\bmod 59)[\because(4,59)=1] \end{array} $ We find that $(3,59)=1$, hence it has unique solution $(\bmod 59)$. Using division algorithm, we obtain $ \begin{array}{l} 59=19 \times 3+2 \\ 3=2 \times 1+1 \end{array} $ Using back substitution, we obtain $ \begin{array}{l} 1=3-2 \times 1 \\ \Rightarrow 1=3-(59-19 \times 3) \times 1 \\ \Rightarrow 1=59 \times(-1)+20 \times 3 \end{array} $ The coefficient of 3 i.e. 20 is the inverse of $3(\bmod 59)$ Now, $ \begin{array}{l} 3 x \equiv 11(\bmod 59) \\ \Rightarrow 20 \times 3 x \equiv 20 \times 11(\bmod 59) \text { [Multiplying throughout by inverse of } 3 \text { i.e. } 20 \text { ] } \\ \Rightarrow(20 \times 3) x \equiv 220(\bmod 59) \\ \Rightarrow x \equiv 43(\bmod 59) \end{array} $ Hence $x \equiv 43(\bmod 59)$ is the solution of the given linear congruence.
Need a full question paper?
Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.