Question

the sum of a 2 digits of 2 digit number is 7.if the digits are reversed,the number formed is 9 less than the original number. what is the original number?

Answer 1

Let the digit at ones place be x
the digit at tens place be y.
therefore the no. is 10y + x
if the digits are reversed then no. is 10x + y
a/q
  x + y = 7  .....(i)
10y + x - (10x + y) = 9
10y + x - 10x - y = 9
9y - 9x = 9
9 (y - x) = 9
y -  x = 1 .....(ii)
on adding eq. (i)  and (ii), we get
 y + x = 7
 y -  x = 1
2y  = 8
y = 4
Now sustitution y = 4 in eq. (i)
x + 4 = 7
x = 3
As we know that no. is 10y + x 
so, the no is
10(4) + 3 = 40 + 3 = 43
so, the original no. is 43