GS. 1 If a number $N$ is chosen randomly from the set of positive integers, the probability of the unit digit of $N^{4}$ being unity is $\frac{P}{10}$, find the value of $P$.
If the unit digit of $N^{4}$ is 1 , then the unit digit of $N$ may be $1,3,7,9$. So the probability $=\frac{4}{10}$ $P=4$