Arithmetic mean of seven observations is 9. If two observations 3 and 8 are added, then find the new mean.

Sure, here are the steps to find the new mean:

1. First, find the total sum of the original seven observations. Since the arithmetic mean is 9, the total sum would be 9 * 7 = 63.

2. Next, add the two new observations to the total sum. So, 63 + 3 + 8 = 74.

3. Now, the total number of observations is 7 original + 2 new = 9.

4. Finally, find the new mean by dividing the new total sum by the new number of observations. So, the new mean is 74 / 9 = 8.22 (rounded to two decimal places).