Answer:
0.335 = 33.5% probability that the student plans to go to medical school
Step-by-step explanation:
What is the probability that the student plans to go to medical school?
Sum of:
40% of 40%(freshmen)
30% of 10%(sophomores)
35% of 30%(juniors)
20% of 20%(seniors)
So

0.335 = 33.5% probability that the student plans to go to medical school
5.
Let x be the age of the father and y be the age of the son. As of today, he's 3 times older, so we have 
10 years ago their ages were, respectively, x-10 and y-10, and the father was 5 times older: 
So, we have the system

Using the first equation, we can substitute every occurrence of "x" with "3y" in the second equation:

So, the son is 20 years old, which means that the father is 60 years old.
Indeed, 10 years ago they were 10 and 50 years old, so the father was 5 times older.
6.
Let x be the age of the grandfather and y the age of the granddaughter. We know that the grandfather is 10 times older: 
He also is 54 years older: 
Again, if we substitute x=10y in the second equation we have

An investment plan that guarantees payments at regular intervals after retirement
:)
The midpoint of 0 and 0.01 is 0.005