Answer:
Answered
Step-by-step explanation:
It is a combbinatorics problem. let's think as we need to do 8 partitions
of these 13 to separate the postcards of different types. So The number of
partitions of n=13 into r=8 terms counting 0's as terms as C(n+r-1,r-1).
(a)
Here n=13 and r=8, put it in the above formula so we get C(13+8-1,8-1)= C(20,7)= 77520 selections.
b).
Here, either (i) we can choose none of type I or (ii) we choose one of type I
Case(i): r=7, n=12 (Here we have only 7 types to choose from)
Case(ii): r=7, n=11 (Here we have only 11 cards to choose and only 7 types to choose them from)
Case (i) + Case(ii) = ,C(12+7-1,7-1) + C(11+7-1,7-1) = C(18,6) + (17,6) = 18564+12376 = 30940 selections.
times radius squared