We see that for every 8 sandwiches that the customer needs, he will pay for 5. Lets see how many groups of 8 sandwiches the order of 675 sandwiches contains. If we do Euclidean Division we see that there are 84 groups of 8 and that three sandwiches are the remainder. 675/8=84.375; Hence we have 84 groups and 0.375*8=3 sandwiches that remain. Thus, the customer would play for 84*5= 420 sandwiches if he had ordered 84 groups of 8 (namely 672 sandwiches). Since he needs another 3 sandwiches and there is no promotional offer for those, he will have to pay in total for 423 sandwiches. It is important to not divide the total number by 8 and then multiply it by 5; the customer gets the free sandwiches only if he completes an offer of 5 sandwiches, thus we have to group the sandwiches in octads and deal with the remainder separately.