Mark has 16 marbles. He puts them into 2 equal groups. How many marbles are in each group.
To find the number of marbles in each group, you need to divide the total number of marbles by the number of groups. In this case, Mark has 16 marbles and he wants to divide them into 2 equal groups.
Therefore, you can use the division operation to find the answer:
Number of marbles in each group = Total number of marbles / Number of groups
Number of marbles in each group = 16 / 2
Calculating this division, you find that each group will have 8 marbles.