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