Suppose your data is in Column A then paste this formula anywhere or in A12 and Press Ctr+Shift+Enter as this is any Array formula ....... After pressing Ctr+Shift+Enter to enter the formula you will see {} will occur around the formula ={SUM(IF(ISERROR(SEARCH("*a*",A1:A10,1)),0,1))} ... never try to enter {} manually ....
Array Formula : After entering the formula Press Ctrl+Shift+Enter
=SUM(IF(ISERROR(SEARCH("*a*",A1:A10,1)),0,1))