1. Needs memorising of last digits of squares from 1-9Here is the list1---------->12---------->43---------->94---------->65---------->56---------->67---------->98---------->49---------->1suppose 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=13Or 10+7= 17 . To determine the correct answer , take average of the sq of extreme digits ieover 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<br />