For this example we will use 25
- Take the "tens" part of the number (the 2 and
     add 1)=3 
 - Multiply the original "tens" part of the
     number by the new number (2x3) 
 - Take the result (2x3=6) and put 25 behind it. Result
     the answer 625.
 
Square of 35
- Take the "tens" part of the number (the 3 and
     add 1)=4 
 - Multiply the original "tens" part of the
     number by the new number (3x4) 
 - Take the result (3x4=12) and put 25 behind it. Result
     the answer 1225.
 
Square of 75
- Take the "tens" part of the number (the 7 and
     add 1)=8 
 - Multiply the original "tens" part of the
     number by the new number (7x8) 
 - Take the result (7x8=56) and put 25 behind it. Result
     the answer 5625.