If 1 + 2 + 3 + ... + n = 325, then what is n?
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20+21+22+23+24+25=325 so n=25
The sum formula : n(n + 1)/2
n(n + 1)/2 = 325, so n(n + 1) = 650, so n = 25
Edit: hope that helped
+267 
