Question

the sum of the digit of a two digit number is 7 when the digits are reversed then the number is decreased by 9 find the number

Answer 1

let the number be xy
sum =x+y=7


10 x+y =the number
10y+x = new number
10x+y=10y+x +9
9x-9y=9
x-y=1
therefore x=1+y
so,
1+y+y=7
2y=6
y=3
therefore x =4
the number is 43