Do the populations have equal variance? Yes, since s1s1 and s2s2 are not that different. How do conclude this? By using a rule of thumb where the ratio of the two sample standard deviations is from 0.5 to 2. (They are not that different as s1/s2=0.683/0.750=0.91s1/s2=0.683/0.750=0.91 is quite close to 1. We will discuss this in more details and quantify what is "close" later in this lesson.)
We can thus proceed with the pooled t-test.
Let μ1μ1 denote the mean for the new machine and μ2μ2 denote the mean for the old machine