Question

the sum of the digits of two-digit number is 7 and if 9 added to the number, the digits are reversed . find the number.

Answer 1

let the digit at ones place be x
digit at tens place is y
No=10y+x
On reversing
digit at ones place=y
digit at trends place=x
new no=10x+y

ATQ
x+y=7.................(1)
and
10y+x+9=10x+y
=> 10x+y-10y-x=9
=>9x-9y=9
=> x-y=1…...........(2)

Solving (1) & (2) for x and y
on adding we get
2x=8
=>x=4

Putting the value of x in (1)
4+y=7
=>y=7-4=3
Number is 34

Answer 2

34

Step-by-step explanation:

Let first digit be x and second digit be y .

Let original no be = 10 x X + Y

A/Q

1.   X + Y = 7

X= 7-Y

2.  10 x X + Y + 9 = 10 x Y + X

10X + Y + 9 = 10Y + X

10X - X + 9 = 10Y - Y

9X + 9 = 9Y

9X - 9Y = -9

X - Y = -1

7-Y-Y = -1

-2Y = -1- -7

-2Y = -8

Y = 4

X = 7-4

 = 3

Original no = 34