my jumping jacks formula!

Problem sum.

Singyan couldnt sleep and she decided to do some jumping jacks to tire herself so as to have a better sleep. For the first set, she did 30 x 8 counts of jacks. Though it was very exhausting, she has the urge to lose those thunder thighs and add an increment of 5 x 8 after each sets. After the fifth set, she felt that she's too tired to continue. How many jumping jacks had she done in total?

solution 1. (the dumb way)...
( (30 x 8) + (35 x 8) + (40 x 8) + (45 x 8) + (50 x 8) ) / 8 = 200 jacks


ANY BETTER SOLUTIONS? OMG, my maths sucks!