Question 902070
<pre>
h = hundreds digit
t = tens digit
u = ones or units digit
100h+10t+u = the number
100u+10t+h = the number reversed
</pre>
The sum of the digits of a three digit number is 13. 
<pre>
h + t + u = 13
</pre>
When 11 is subtracted from the sum of the hundreds digit and tens digit, the answer is equal to the units digit. 
<pre>
 (h+t) - 11 = u
 h + t - 11 = u
  h + t - u = 11 
</pre>
Additionally, when the digits are reversed, the new value is 495 less than the original number.
<pre>
    100u+10t+h = (100h+10t+u) - 495
100u + 10t + h = 100h + 10t + u - 495
     99u - 99h = -495                 <-- divide thru by 99 
         u - h = -5                   <-- get in h,t,u order 
        -h + u = -5                   

{{{system(h + t + u = 13, h + t - u = 11,-h + u = -5)}}}

Can you solve that system?  If not post again asking how.

The number is 661 

Edwin</pre>