Try:
SELECT AVG(TB1_PRC) FROM Table1 WHERE TB1_DT BETWEEN '2013-08-05' AND '2013-08-10'
"Maciej Los has posted a comment to the Answer "sum of row value date wise":
Paul, please have a look at the structure of database... All fields are varchar data types. A bit of comment on that?
"
Maciej is absolutely right - it won't work as given if you store your dates in text form: so don't. Always store data in the most appropriate format: for dates that is DateTime or DateTime2, becaue keeping them in any other format is going to give you headaches. Text is a particularly poors choice for two main reasons:
1) The sort order is wrong:
1/12/2013
2/12/2012
28/12/2013
3/12/2013
2) Text dates imply that they are entered as text in some form from a different system or systems - which may not all share the same locale and thus have different date formats: how are you going to cope with
1/12/2013
12/1/2013
2013-12-1
13/12/1
12-1-13
1st Dec '13
Storing dates in a date field solves these problems provided they are passed to SQL as DateTime values rather than strings - as they should be anyway to prevent SQL Injection attacks.
Change your database, then use the code above.