Question 901333
<pre>
  XY
 <u>+YX</u>
  99

To add two numbers and get an odd number like 9, one has to be 
odd and the other even.  And since one is twice the other and they
add to 9 they can only be 3 and 6.  So it could be either

  36      63 
 <u>+63</u>  or <u>+36</u> 
  99      99

It's either 36 or 63.

Edwin</pre>