數學題．．．急

設十位數字 為a
設個位數為b

十位數字與個位數字之比為4:1
=> a : b = 4 : 1
=> a = 4 x b

原數 是 (10 x a + b)

將原數加２之和除以３，必等於數字倒換所成的新數

=> ( (10xa + b) + 2 ) /3 = 10x b + a
=> 10a + b + 2 = 30b + 3a
=> 10 (4b) + b + 2 = 30 b + 3 (4b) ______ 因為 (a = 4 x b)
=> 41b + 2 = 42 b
ans: b = 2
and a = 4x b = 8

原數 : 82

let the x be the unit digit, so 4x is the 10 unit digit
so the number is 4x * 10 + x = 41x
(41x + 2) /3 = 10x + 4x
41x + 2 = 42x
x=2
the number is 82