According to Hellin's law chances of twins in pregnancy are:: (A) 1 in 60, (B) 1 in 70, (C) 1 in 80, (D) 1 in 90
Answer is C. According to Hellin’s rule
The mathematical frequency of multiple pregnancy is:

Twins 1 in 80
Triplets 1 in (80)2
Quadruplets 1 in (80)3 and so on