Respuesta :

Prohor

Answer:

20 students offered both physics and biology.

Step-by-step explanation:

n(Total) = 50

n(Physics) = 40

n(Biology) = 30

Let n(Physics and Biology) = x

n(Physics only) = 40 -x

n(Biology only) = 30 - x

40 - x + 30 - x + x = 50

70 - x = 50

x = 20
20 students are in biology and in physics