In a transistor if α varies between 20/21 and 100/101, then the value…

The $α$ and $β$ are related by the relation $β=\frac{α}{1-α}$

For $α=\frac{20}{21}$

$β=\frac{\frac{20}{21}}{1-\frac{20}{21}}=\frac{\frac{20}{21}}{\frac{1}{21}}=20$

For $α=\frac{100}{101}$

$β=\frac{\frac{100}{101}}{1-\frac{100}{101}}=\frac{\frac{100}{101}}{\frac{1}{101}}=100$

Thus the value of $β$ lies between 20 – 100.