We are given that there are a total of 78 students. If we set the following variables:

Then, the sum of all of these must be 78, that is:

Since there are 15 in chemistry and physics and 47 in chemistry, we may replace that into the equation and we get:

Simplifying:

Now we solve for P by subtracting 62 on both sides:

Therefore, there are 16 students in physics
Answer:
√S(S-A)(S-B)(S-C)
Step-by-step explanation:
S=(A+B+C)\2
where S= semi-perimeter
A,B and C are unequal length of triangle.
Andre walks for 16 minutes. 80% of 10 is 8 and times that by 2 is 16 so 16 minutes.