Question

The sum of the digits of a two digit number is 12 . If the digits are reversed , the new number is 12 less than double the original number. Find the number

Answer 1

original number:
let the unit digit be x
let the tens digit be y
the number is 10y + x

new number:
unit digit ---- y
tens digit ---- x
new number is 10x+y

new number < twice original number by 12

10x+y = 2(10y+x) - 12
10x+y = 20y + 2x - 12
8x - 19y = -12

but x+y=12 ----> y = 12-x

I would use substitution to solve.
Let me know what answer you get for checking