you are getting confused becuase they really did pay $27 for it
the fact is they outlayed $10 each and recieved $1 back, its $9 each. thats the effective price the three men paid for the radio
the percentages are getting jumbled because the boy pocketed $2.
the dollar goes missing if you multiply the effective cost when you do a minus first. its called the "ORDER OF OPERATIONS" (i.e, multiply and divide before adding and minus) for a reason.
