The numbers on a single die are 1,2,3,4,5 and 6 . So, the mean =‌
1+2+3+4+5+6
6
=‌
21
6
=3.5 When multiple dice are thrown, the mean of the sum of the numbers appearing on them = the sum of means of individual dice. Since, each die has mean 3.5. So, the mean of the sum of the numbers appearing on three dice =3.5+3.5+3.5=10.5