Period 1 had actual sales of 1,020. period 2 had actual sales of 1,010, and period 3 had actual sales of 1,060. what is the three-period moving average? select 2. our last four periods had sales, from oldest to most recent, of 100, 200, 130, and 300. what is the three-period ma? select 3. last month our forecast was 800, but we sold 1,000 units. what is the forecast error? select 4. last month, the forecast error was -300. with an alpha of .10, by how much will this month's forecast change? select 5. the last two months had forecast errors of 200 and -50; what is the mad? select 6. we find our data has a trend, with intercept a=90 and slope b=2. at time 6, what is the forecast?