Question 8481
if you don't know it, think of the squared numbers that you already know and use them as markers...


for example, you might already know that {{{12^2}}}=144 and you might already know that {{{15^2}}}=225.  if so, you know that 169 would be between these numbers.  so it would either be 13 or 14  


Look at the ending...169 ends with a 9. 
if we multiply by 4*4, the ending number will be 6 AND we also know that when we multiply even numbers, the ending number will NEVER end with an odd number like 9.  


We know that when we multiply 3*3, it ends in 9. 
Then you know that 13*13 would be a good match. 
{{{13^2}}}=169


You can try to memorize some or just take an educated guess when playing with numbers.