Question

The sum of the digit in a 2-digit number is 7 . If 9 is subtracted from the number, it's digits are reversed. Find the number.

Answer 1

Answer:

let the number is xy means 10x+y

sum of the digits is 7

so, x+y=7

10x+y-9 =10y+x

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

=> 9x-9y=9

=> 9(x-y)=9

=> x-y=9/9 =1

=> x=1+y

x+y=7

=> 1+y+y=7

=> 2y=7-1=6

=> y=6/2=3

x=3+1=4

so the number is 43

Answer 2

Answer:

43

Step-by-step explanation:

Let the digit in units place be 'x' and that to in tens place be 'y' .

Thus , the original number is 10y + x .

From first condition , x + y = 7 --------(1)

From second condition ,

10y + x - 9 = 10x + y

9y - 9 = 9x

y - 1 = x

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

Solving (1) & (2) simultaneously , we get

y = 4 & x = 3

Thus the original number is 43