To calculate the 3-period moving average for the 4th week, we take the average of the time series values from the three previous weeks (1st, 2nd, and 3rd weeks).
The values for the three weeks are:
- Week 1: 21.00
- Week 2: 17.00
- Week 3: 18.00
Now, we calculate the 3-period moving average:
\[ \text{Moving Average} = \frac{\text{Value Week 1} + \text{Value Week 2} + \text{Value Week 3}}{3} \]
Substituting the values:
\[ \text{Moving Average} = \frac{21.00 + 17.00 + 18.00}{3} = \frac{56.00}{3} \approx 18.67 \]
Rounding to 1 decimal place, the 3-period moving average forecast for the 4th week is:
18.7