Query bank balance dr. cr.

In a question Cash at Bank on 1-4-2007 Rs. 50000 (Cr.) On 31-3-2008 Rs. 80000 (Dr.) Make bank account Ans:- in a ans Brought down balance show in credit side By bal. b/d 50,000 My query is why brought down balance show in cr. Side of bank a/c In a question given 50,000 Cr. Balance which mean deposit available in bank Then it will show Dr. Side of Bank a/c as To bal. b/d 50,000 Why in ans show Cr. Side of Bank a/c as By bal. b/d 50,000