There are 7 marbles laying across the ground, you decide to pick them up so that they don't become a problem later. Afterwards, you find that your friend has made it into a competition to see who can get the most marbles. Both of you get 40 marbles each, this means there is a total of 8 groups of 10 marbles, and 7 groups of individual marbles. You then rejoice, as the marble minefield is now gone.