A uniform disc is rotating with angular velocity $\omega$ and then it is gently placed **horizontally** on a rough horizontal surface having a coefficient of friction $\mu$ .
The total time $T$ taken by disc to stop rotating completely can be expressed as

$T\quad =\cfrac { a }{ b } \times \cfrac { \omega R }{ \mu g }$.

Find The value of $a\times b$.

**Details:**

$\bullet$ 'a' and 'b' are Co-prime positive integers.