7-11-13 trick

To multiply a number by 7 x 11 x 13
Just write down a three digit number and write it twice.
For eg:- 231 x 7 x11 x 13
write 231 twice
i.e. 231231
Yes !!! This is the desired answer after multiplying 231 by 7-11-13
Simple enuf !! Yeah ???

Square of nos. ending in 5

Just multiply the first digit of number with its consecutive number and write the product with suare of 5.

Eg 1:- Square of 35 :-
3*4=12
5^2=25
Hence, Square of 25 is 1225

Eg 2:- Square of 75:-
7*8=56
5^2=25
Hence, square of 75 is 5625