Answer:
Groups with more diverse members are effective at solving difficult problems because they leverage the different opinions and outlooks of the group members.
A group with diverse members will have more types of solutions for a people as the thinking of every person from the group will be different. Hence, they will have better options for solving different problems.
In contrast, a group which does not have diversified members will have less solution options for different problems as the thinking of them will be closely elated to each other. Hence, they won't be as effective in solving problems.