Question

a number consists of two digits whose sum is 9.if 9 is subtracted from the number its digits are interchanged .fiind the numbers

Answer 1

let any number = 10x + y

where x is tens digit and y is unit digit .

now,
x + y = 9 ------(1)


again,

10x + y -9 = 10y + x

9x - 9y = 9

x - y = 1 --------(2)

solve equations (1) and (2)

x = 5 and y = 4

so, number = 10x 5 + 4 = 54