Question

The sum of the two digits of a two digit number is 15. If 9 is added to the number the digits are reversed. What is the number

Answer 1

Hello,

let to be 10' digit number x
let to be 1' unit digit no y

then
a/q

x+y=15

10x+y+9=10y+x
10x-x+y-10y=-9

9x-9x=-9

9(x-y)=-9
x-y=-1


then,

solving the equations :-----

x+y=15
x-y=-1

______
2y=16

y=16/2=8

then,
x+y=15
x+8=15
x=15-8
x=7
then

10y+x
10*8+7

80+7
87




that's all


by sujeet yaduvanshi.

Answer 2

let the digits be x nd y

ATQ

x+y=15..........................eq 1

original no=10x+y

when digits are reversed it becomes (10y+x)

ATQ

10y+x=10x+y+9

10y-y+x-10x=9

9y-9x=9

9(y-x)=9

y-x=1

y=1+x...............eq 2

from eq 1 nd 2 we get

x+y=15

x+1+x=15

2x=14

x=7

y=8

hence required no is 78