Question

A certain no. between 10 and 100 is 8 times the sum of its digit.......

Answer 1

Complete the question once then this.

let the number be x & y 
value of number = 10x+y 
10x+y = 8(x+y) 
10x+y =8x+8y
2x-7y=0....................(1) 
10x+y-45 = 10y+x 
9x-9y=45 
x-y = 5.................(2) 
multiply by -2
-2x+2y=-10
add to (1) 
-5y=-10
y=2 
x-y =5 
x=7 
Number = 72