Question 604790
a number is made up of two digits. The sum of the digits is 11. if the digits are interchanged, the original number is increase by 9. Find the original number
**
let u=units digit
let t=tens digit
..
u+t=11
t=11-u
original number=10t+u
interchanged number=10u+t
..
10u+t=10t+u+9
sub (11-u) for t
10u+11-u=10(11-u)+u+9
10u+11-u=110-10u+u+9
18u=108
u=6
t=11-u=5
ans:
original number 
=10t+u
=50+6
=56