```
# DarkCoder
def sum_of_series(first_term: int, common_diff: int, num_of_terms: int) -> float:
"""
Find the sum of n terms in an arithmetic progression.
>>> sum_of_series(1, 1, 10)
55.0
>>> sum_of_series(1, 10, 100)
49600.0
"""
total = (num_of_terms / 2) * (2 * first_term + (num_of_terms - 1) * common_diff)
# formula for sum of series
return total
def main():
print(sum_of_series(1, 1, 10))
if __name__ == "__main__":
import doctest
doctest.testmod()
```