Common difference d = 13/4-2=5/4; d = 9/2-13/4=5/4.
In general, a, a+d, ..., a+49d is the series up to the 50th term (a is the first term).
Take these in pairs to find the sum:
(a+a+49d)+(a+d+a+48d)+...
(2a+49d)+(2a+49d)+...
There are 25 pairs: sum=25(2a+49d).
a=2, d=5/4, sum=25(4+245/4)=100+6125/4=1631.25.