You need to order 4 plastic cups for each of the 800 runners. Plastic cups are sold in 2 different pack sizes and you must choose one type of pack only. A pack of 500 costs £12.50 or a pack of 800 costs £23.20
What is the least amount of money it will cost to provide 4 cups to each runner?
4 cups for each runner: $4 \cdot 800 = 3200$ cups in total. $3200 / 500 = 6.4$ ( so at least 7 packs of 500)
$3200 / 800 = 4$ ( so at least 4 packs of 800)
$$7 \cdot 12.50 = 87.5£$$
$$4 \cdot 23.20 = 92.8£$$