Answer: 
Step-by-step explanation:
The probability that 4 are chem majors would be 5%
Sum/difference:
Let
This means that
Now, assume that 
is rational. The sum/difference of two rational numbers is still rational (so 5-x is rational), and the division by 3 doesn't change this. So, you have that the square root of 8 equals a rational number, which is false. The mistake must have been supposing that was rational, which proves that the sum/difference of the two given terms was irrational
Multiplication/division:
The logic is actually the same: if we multiply the two terms we get
if again we assume x to be rational, we have
But if x is rational, so is -x/15, and again we come to a contradiction: we have the square root of 8 on one side, which is irrational, and -x/15 on the other, which is rational. So, again, x must have been irrational. You can prove the same claim for the division in a totally similar fashion.
The line of sight is the hypotenuse of a right triangle with short leg 400 m, 90 degree angle where the short leg meets the ground, an 83 degree angle at the top, and a 7 degree angle across from the right angle on the ground. Because this 7 degree angle is an alternate interior angle with the angle of depression, they are the same degree measure. Looking for the hypotenuse, we use the sin ratio: sin (7) = 400/x.
