(1) The first group is intuitive and accurate.

The first group variance: 2 and the second group variance: 5.2.

Because the larger the variance, the more unstable it is, so the first group is more correct.

2. The average value is (42+39+39+33+27+24)/6=34.

So fill in the blanks: 8 5 5-1 -7-10.

64 25 25 1 49 100

The variance of six grades is (64+25+25+1+49+100)/6 = 44.