As shown in the figure, sum the symbols and arrange the combined symbols respectively. The first is the summation symbol, which is expanded as follows:
Summation extension
Secondly, the symbols of permutation and combination are expanded as follows:
Arrangement calculation method
(2) The sum symbol is high school knowledge, and the permutation and combination is the probability part of high school.
References:
Sum symbol: Web link
Permutation and combination: network links