This is a bit of a strange one, so bear with me. Co-op are running an offer where you can buy 6 of Refreshers bars, Drumstick bars or Sherbet Dib Dabs for 50p. Due to the fact that the Dib Dabs are 15p and the Bars are 10p, you get more of a discount if you just buy the bars. The till takes 40p off, regardless of which ones you purchase, so 6 x 10p - 40p = 20p. Bargain!