Question

a) 1+2+3...+80 =
b)1+2+3...+250=
c)1+2+3...+1000=
d) 1+2+3...+50=
e)1+2+3...+618=

Answer 1

$\displaystyle a)1+2+3+...+80 = \frac{80(80+1)}{2} = \frac{80 \times 81}{2} = \frac{6480}{2} =3240 \\ \\ b)1+2+3+...+250= \frac{250(250+1)}{2} = \frac{250 \times 251}{2} = \frac{62750}{2} =31375 \\ \\ c)1+2+3+...+1000= \frac{1000(1000+1)}{2} = \frac{1000 \times 1001}{2} = \\ \\ = \frac{1001000}{2} =500500 \\ \\ d) 1+2+3+...+50= \frac{50(50+1)}{2} = \frac{50 \times 51}{2} = \frac{2550}{2} =1275$

$\displaystyle e)1+2+3+...+618= \frac{618(618+1)}{2} = \frac{618 \times 619}{2} = \frac{382542}{2} =191271$

Answer 2

a)=86
b)=256
c)=1006
d)=56
e)=624
sper ca ti-am fost te folos !