Question

seven times a two digit number is equal to four times the number obtained by reversing the order of its digit if the difference of the digit is 3 determine the number

Answer 1

let the two digit no. be  10x + y 

then 7 (10 x +y) = 4(10y + x)        

 ------------> 70 x + 7y = 40y + 4x            

  -------> 66x = 33y  

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

y -x = 3     ....(2)

2x -x =3  (substitute the value of y from (1) )

  x =3 

or, y -3=3         y = 6

so the no.  10x +y = 10*3 + 6 = 30 +6 = 36

Answer 2

Let the ten’s and the unit's digit be y and x  respectively.

So, the number is 10y + x.

The number when digits are reversed = 10x + y

Hence,

7 (10y + x) = 4(10x + y)

⇒ 2y = x

Also x - y = 3 …(ii)

Solving (i) and (ii), we get

y = 3 and x = 6.

Hence, the number is 36.