Sum of first 50 terms

The sum of the first 50 terms of an arithmetic series is 100. If the common differenc is 2, what is the first term?
i keep getting -23 but its not right......... :(

The sum of an arithmetic sequence is given by

Sn= n[(a1 +an)/2]

100= 50 [(a1 + an)/2]

a1=2 + a0
an=100+a0

100= 50 [102+2a0)/2]

2=[(102+2a0)/2]
4=102 + 2a0
-98=2a0
a0=-49

so add 2 to that and u get

a1=-47

an=dn+a0
an=2(n)-49
a0= the term before a1

Use Sn=n/2(2a+(n-1)d)

Now, sub in what you know. You know the sum (Sn) =100, and that the difference is 2 (d). You also know that n (the number of terms) is 50.

100=50/2(2a+(50-1)2)

100=25(2a+98)
100=50a+2450
-2350=50a
a=-47