To find the fourth number in the group, we can use the formula for the average:

$\text{Average} = \frac{\text{Sum of all numbers}}{\text{Number of numbers}}$

Given:

• Average = 14
• First three numbers = 11, 12, 15
• Number of numbers = 4

1. Calculate the total sum of the four numbers: $14 = \frac{\text{Sum}}{4} \implies \text{Sum} = 14 \times 4 = 56$

2. Calculate the sum of the first three numbers: $11 + 12 + 15 = 38$

3. Now, let $x$ be the fourth number: $38 + x = 56 \implies x = 56 - 38 = 18$

Thus, the fourth number is 18.

Would you like more details or do you have any questions? Here are some related questions to consider:

1. How do you calculate the average of a different set of numbers?
2. What happens to the average if one of the numbers changes?
3. Can you find the average of a group of five numbers?
4. How do you determine if a number is an outlier in a set?
5. What methods can be used to represent data averages visually?

Tip: Always double-check your calculations by substituting back into the average formula!