Packets of crisps are normally 50 cents each at my local shop. in a hurry yesterday, i went into
the shop, picked up 8 packets of crisps, gave the assistant $4 and headed for the door. the
assistant called me back to give me 80 cents change. “special offer this week,” she explained.
which one of the following offers would not explain the 80 cents change i received?
a. all packets 20% off
b. buy 2 packets, get a third packet for 10 cents
c. buy 3 packets, get a fourth packet for 10 cents
d. buy 4 packets, get a fifth packet free

need correct answer and explanation - ty