Question

A number consists of two digits whose sum is 8. If 18 is added to the number, its digits get interchanged. Find the number.

Answer 1

let numbers be x and y
one no = x another number = 8-x
XY +18 = yx
XY = x × 10 + 8-x × 1
XY = 9x + 8
yx = (8- x )× 10 + x × 1
yx = 80 - 10x + x
yx = 80 - 9x

so
XY + 18 = yx
9x + 8 + 18 = 80 - 9x
9x + 9x = 80 - 26
18x = 54
x = 54/18
x = 3
y= 5
the number is 35