PHP正则表达式格式？

I am trying to write a regex format to check the following type string:

40/4

The following features I need:

• the string will be exactly four characters long
• 1st character will have to be 1-9
• 2nd character will have to be 0-9
• 3rd character will have to be a forward slash (/)
• and 4th character will have to be 0-9

Here's what I ended up writing:

"/^.{4}$[1-9][0-9][\/][1-9]/"

Please help me to write the correct format.

Thanks

It will be like below:

/^[1-9][0-9]\/[0-9]$/