In binary we have normalized number of the form $(-1)^{S} \times 1.M \times 2^{E-\text{ Bias}}$ where,
- $S:$ sign bit
- $M :$ Mantissa
- $E:$ Exponent
Similarly for for $\textsf{Binary Coded Decimal (BCD)}$ numbers the normalized number representation will be $:(-1)^{S} \times 1.M \times 10^{E-\text{ Bias}}$
Here bias is given to be excess - $50$ meaning that we need to subtract $50$ from the base exponent field to get the actual exponent.
So, maximum mantissa value with $4\;\text{BCD}$ digits $= 9999$
Maximum base exponent value with $2\;\text{BCD}$ digits $= 99$
So, maximum actual exponent value possible with $2\;\text{BCD}$ digits $= 99\;\text{- Bias} $
$\qquad \qquad \qquad = 99 - 50$
$\qquad \qquad \qquad = 49$
So, the magnitude of the largest positive number $= 9.9999 \times 10^{49}$
Similarly,
To get a minimum positive number, we have to set mantissa $= 0$ and exponent field $= 0$
So, doing that we get exponent $= 0 - 50 = -50$
So, magnitude of minimum positive number $= 1.0000 \times 10^{-50}$
Therefore, maximum positive number $ = 9.9999 \times 10^{49}$
Minimum positive number $= 1.0000 \times 10^{-50}$