One set of numbers has an average value of 4, and another set of numbers has twice the number of the first set of numbers and its average value is 10. Combine these two sets of numbers, what is their average value?
有一组数的平均值等于4，另一组数的个数是第一组数的两倍且其平均值等于10．合并这二组数，请问它们的平均值等于多少．
<result>8</result>