You want to lear to do multiplication of number with a 5 in the end?
e.g 35x35=?
easy: 1225
here is the trick:
take the first number (3) and multiplicate it with itself plus one (4), that gives 12, then ad 25 to the end. and you got 1225
another one:
65x65
take the first number (6) and multiplicate it with itself plus one (7), that gives 42, then ad 25 to the end. and you got 4225
answer:4225
easy, isnt it?