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KCET · Maths · Mathematical Reasoning

The greatest value of \(\mathrm{x}\) satisfying \(21 \equiv 385\) \((\bmod x)\) and \(587 \equiv 167(\bmod x)\) is

  1. A 156
  2. B 32
  3. C 28
  4. D 56
Verified Solution

Answer & Solution

Correct Answer

(C) 28

Step-by-step Solution

Detailed explanation

We know that,
\(\quad \mathrm{a} \equiv \mathrm{b}(\bmod \mathrm{x})=\frac{(\mathrm{a}-\mathrm{b})}{\mathrm{x}}\)
Given, \(\quad 21 \equiv 385(\bmod \mathrm{x})=\frac{(21-385)}{\mathrm{x}}\)
\(=-\frac{364}{\mathrm{x}} \quad \text{...(i)}\)
and \(587 \equiv 167(\bmod x)\)
\[
=\frac{(587-167)}{x}=\frac{420}{x} \quad \text{...(ii)}
\]
Now, the greatest value of ' \(x\) ' satisfying Eq. (i) and Eq. (ii) \(=\max [\mathrm{LCM}\) of \((364,420)\) ]
\[
\begin{array}{ll}
\Rightarrow & x=\max (13,15,28) \\
\Rightarrow & x=28
\end{array}
\]