A simple calculation method for 1 + 3 + 6 + 10 + 15 + 21 + 28. + 4950 + 5050

A simple calculation method for 1 + 3 + 6 + 10 + 15 + 21 + 28. + 4950 + 5050


General term an = 1 + 2 + 3 +... + n = n (n + 1) / 2 = n & # 178; / 2 + n / 2
Sn= ( 1² + 2² +3² +...+n² ）/2 +( 1+2+3+...+n)/2
= n(n+1)(n+2)/6
S100= 171700



1/3+1/16+1/10+1/15+1/21+1/28
I've seen your answer, but I want a process


1/3+1/16+1/10+1/15+1/21+1/28
=1/3+(1/10+1/15)+(1/21+1/28)+1/16
=1/3+1/6+1/12+1/16
=1/2+1/12+1/16
=7/12+1/16
=31/48



How to calculate 62.5-21.7-28.3


62.5-21.7-28.3
=62.5-（21.7+28.3）
=62.5-50
=12.5

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