Thanks to the CD-Rom i bought for N, he has learnt how to add double digits. I just showed him how it is done and left him on his own. He's been playing this activity daily and has been getting the right answers.
A few nights ago, i asked him what 12+12 was. He wasn't able to answer nor visualised the working format. Today, i wrote the equation on the doodle board, this time in working form. I showed him that he's to add the same way as the game. Subsequently, i asked him to calculate 13+13, this time without any visual aid. He quietly added the sum mentally and gave 26 as the answer! We did a few sums and he was able to give me the right answers-all calculated in his head.