Question 509226
The sum of the digits of a certain two digit number is 7. Reversing its digits increases the number by 9. What is the number? 
----
Let the number be 10t+u where t is the tens and u is the units digit.
---
Equations:
t + u = 7
(10u+t)-(10t+u) = 9
----
Rearrange:
t + u = 7
-9t+9u = 9
----
Modify:
t + u = 7
t - u = -9
----
2t = -2
t = -1
----
Comment: That cannot be.
----------------------------------  
It looks like reversing the digits DECREASED the value rather thaen INcreased
the value.
===============
Cheers,
Stan H.
=====================