Calculate the Average Change: Adding 1 to the Set {2,3,4,5}

To solve this problem, we'll begin by calculating the average of the original group of numbers ($2, 3, 4, 5$):

1. Calculate the sum of the original group: $2 + 3 + 4 + 5 = 14$.

2. Determine the number of elements in the original group: $4$.

3. Calculate the average of the original group: $\frac{14}{4} = 3.5$.

Next, we'll calculate the average after adding the number $1$ to the group, forming the new group ($1, 2, 3, 4, 5$):

1. Calculate the sum of the new group: $1 + 2 + 3 + 4 + 5 = 15$.

2. Determine the number of elements in the new group: $5$.

3. Calculate the average of the new group: $\frac{15}{5} = 3$.

Finally, compare the two averages:

The average of the original group is $3.5$, while the average of the new group is $3$.

The average decreases when the number 1 is added to the group.

Therefore, the solution to the problem is that the average will decrease.