Mentally Square any numbers between 51 to 59.

• Step 1) :- Subtract 50 from the number
• Step 2) :- Add the result from first step to 25.
• Step 3) :- Square the result from first step (Append zero if result is single digit). 
• Step 4) :- Place result from third next  result from step second. 

Examples,
     1) (53)^2
     Step 1) :- 53 - 50 = 3
     Step 2) :- 25 + 3 = 28
     Step 3) :- 3 * 3 = 09.....(Append Zero)
     Step 4) :-  = 2809

 So we get, (53)^2 = 2809.

     2) (54)^2
     Step 1) :- 54 - 50 = 4
     Step 2) :- 25 + 4 = 29
     Step 3) :- 4 * 4 = 16
     Step 4) :-  = 2916

 So we get, (54)^2 = 2916.

     3) (57)^2
     Step 1) :- 57 - 50 = 7
     Step 2) :- 25 + 7 = 32
     Step 3) :- 7 * 7 = 49
     Step 4) :-  = 3249

So we get, (53)^2 = 3249.

Best Luck👍😊