Out of his 8 children, 2 have only 5 children so the rest who have 8 ( the same number as him) are 8-2 = <<8-2=6>>6
6 of Max's children have 8 children each for a total of 6*8 = <<6*8=48>>48 grandchildren
2 of Max's children have 5 children each for a total of 5*2 = <<5*2=10>>10 grandchildren
In total he has 48+10 = <<48+10=58>>58 grandchildren
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