Question

hey! m-ajutati plz.?
5+10+.....+1000=

Answer 1

Notam suma cu S
S = 5+10+........1000
S = 1000+995+ .....+5
_________________
2S = 1005+1005+........+1005              nr. =  (ultimul - primul) : pas+1
                I___________I                                 1000-5:5+1=200
                     de 200 ori
2S = 200*1005
S = 200*1005:2 = calculezi tu

Answer 2

$\displaystyle 5+10+...+1000=5(1+2+...+200)=5 \times \frac{200(200+1)}{2} = \\ \\ =5 \times \frac{200 \times 201}{2} =5 \times \frac{40200}{2} =5 \times 20100=100500$