Question

aflati nr nat x daca: 
3+6+9+......297=150x

Answer 1

3+6+9+.....+297=150x
3(1+2+3+4+5+.....+99)=150x
1+2+3+4+5...+99=150x:3=50x
(99*100):2=50x
9900:2=50x
4950=50x
x=4950:50
x=99

Answer 2

3+6+9+...+297=150x
150x=99*(3+297):2
150x= 99*300:2
150x= 99*150
150x=14850 / :150
x= 99