The sum o the digits of a two-digit number is 6. The number with the digits interchanged is 3 times the tens digit of the original number. Find the original number.
in original number:
tens digit --- x
unit digit --- y
x+y = 6 ---> y = 6-x
original number: 10x + y
number reveresed: 10y+x
10y + x = 3(x)
10y = 2x
10(6-x) = 2x
60 - 10x = 2x
-12x = -60
x = 5
y = 1
original number: 51