Math
posted by Anonymous .
Noreen recently took a job helping people register to vote. The job has a mandatory 10day period of probation during which her success rate is strictly monitored. On her first day, she registered 30 people. Then, for each of the next 9 days, she registered 4 more people than she did on the previous day. How many people did she register altogether during her probationary period?
F. 300
G. 340
H. 480
J. 560
K. 600

arithmetic series
see
http://www.mathwords.com/a/arithmetic_series.htm
here a1 = 30 and d = 4 and n = 10 
I still don't get it.