Re: So you think ur CLEVER?
Its all how the ques. is asked
When the friends paid $10 (or pounds) each, they had paid $30 in total
When the shop-keeper gave $5 to the delivery driver, the 3 friends had paid $25 to the shop-keeper and $5 to the delivery driver for the delivery. <------ This is the tricky part, 25+5= 30 (total cost)
Now when the delivery driver gave them $3 each, the friends had paid $25 to the shop-keeper and $2 to delivery driver $25+$2 = $27 = 3 x $9.
27+3(that the driver gave them back)=30
SOLVED ;)