Sq root trick with nos above 100

Needs memorising of last digits of squares from 1-9

Here is the list

1---------->1
2---------->4
3---------->9
4---------->6
5---------->5
6---------->6
7---------->9
8---------->4
9---------->1

suppose the no is 169, then take the hundreds value (over here 100 and key in its sq rt ie 10)

now observe the last digit . Thats the same ending for 3 and 7 . so the no is either 10+3=13
Or 10+7= 17 . To determine the correct answer , take average of the sq of extreme digits ie
over here (10'2 + 20'2) /2 = 250. In our case 169<250 . Therefore the answer will be 13 .

If here the problem number was greater than 250 then the answer would have been 17