At Webster High School, the ratio of males to females writing the Pascal Contest is $3: 7$. If there are 21 males writing the Contest, what is the total number of students writing?
(A) 30
(B) 25
(C) 49
(D) 70
(E) 79
Since there were 21 males writing and the ratio of males to females writing is $3: 7$, then there are $\frac{7}{3} \times 21=49$ females writing.

Therefore, the total number of students writing is $49+21=70$.

ANSWER: (D)