The tv was £30 pounds which the women originally paid.
Having realised the tv should`ve been £25 pounds the assistant refunds the women £3 which means the women have paid £27 pounds for a £25 pound tv.
In other words they have paid £2 pounds too much and that`s why the assistant as pocketed the £2 pounds. He obviously didn`t actually tell the women it was only £25 pounds.
30-5=25+3=28+2=30. The trick is remembering the women paid £2 pounds too much. As the actual price paid for the tv was £27 pounds and not £25 pounds.
Regards Howard