Question

a certain no. of 2digits is 4times the sum of its digits. if 9 is added to the no. the digits in the no. are reversed. Find the no.

Answer 1

Answer is 12
as (1+2=3) and (3×4=12)
if 9 is added to 12 it comes 21 which is the reversed form of 12

Answer 2

Let
Ten's place digit =x
Unit's place digit=y
The original number= 10x+y----(1)
Reversing the digits=10y+x---(2)
Given
10x+y=4(x+y)
10x+y-4x-4y=0
6x-3y=0
Divide each term with 3
2x-y=0
Therefore
2x=y---(3)
If 9 is add to (1)=(2)
9+10x+y=10y+x
9+10x-x=10y-y
9+9x=9y
Divide each term with9
1+x=y
1+x=2x from(3)
1=2x-x
1=x
Put x=1 in (3)
2=y
Therefore
Required number=10x+y
=10×1+2
=10+2
=12