In a transistor if $α$ varies between $\frac{20}{21}$ and $\frac{100}{101}$, then the value of $β$ lies between:

20 – 100

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.