Question

calcule quantos numeros impares existem entre 2 e 1000 e calcule a soma deles

Answer 1

$a1=3\\ an=999\\ r=2\\ \\ an=a1+(n-1)r\\ 999=3+(n-1)2\\ 999-3=2n-2\\ 996=2n-2\\ 996+2=2n\\ 998=2n\\ \frac { 998 }{ 2 } =n\\ \\ 499=n\\ \\ \\ Sn=(\frac { a1+an }{ 2 } )n\\ \\ Sn=(\frac { 3+999 }{ 2 } )499\\ \\ Sn=(\frac { 1002 }{ 2 } )499\\ \\ Sn=501*499\\ Sn=249.999$