1+2+3….+49+50=s berapa s?

50/2(2.1+(50-1)1)
25(2+(49.1)
25(2+49)
25.51
1275

[(50 – 1 + 1) x (50 + 1)] : 2 x 1
[50 x 51] : 2
2550 : 2 = 1275
Jadi, s = 1275