Raymond B. answered 01/22/23
Math, microeconomics or criminal justice
sum of 1+2+3+...+99+100 = 100(101)/2 = 50(101) = 5050
Gauss' formula is n(n+1)/2 for adding up the integers from 1 to n
construct pairs of the 1st and last integers,
then the 2nd and 2nd to last
then the 3rd and 3rd to last
etc.
each pair sums to 101. there are 100/2 such pairs
half as many pairs as integers
multiply 101 times 100/2 = 5050