How many $2$ digit even numbers can be formed from the digits $1,2,3,4,5$ if the digits can be repeated?

Step $1:$
Finding different number of ways.
For $2$ digits even number, only $2$ digits are possible at unit place $2$ or $4$ and at tens place all $5$ digits are possible.

Step $2:$
Using multiplication principle.
Total number of $2$ digit even number $=2\times 5=10$
Hence, Number of $2$ digit even numbers $=10$