How can we solve this below questions without help of paper and pen?

Lets see:

1) 11263*11=123893

Simplification:

copy the first 1 then add fist digit with the next digit

i.e.1,1+2 means 12

STEP 1 copy first digit 1

STEP 2 1+1=2

STEP 3 1+2=3

STEP 4 2+6=8

STEP 5 6+3=9

and then copy the last.3

Answer is 123893.

2) 23569*12

Simplification :

STEP 1 copy the first digit 2

STEP 2 2*2=4+next digit (3)7

STEP 3 3*2=6+5=11 here 1 is add as carry in digit 7

STEP 4 5*2=10+6=16

STEP 5 6*2=12+9=21

STEP 6 9*2=18

271618

+1121

282828 Answer