Soln to 1st question:
Let the no. of male student is x and female student be y, thus total no of student is = x+y
Ques gives information that 72% of X and 80 % of Y applied for the college and asks what is x/x+y
Statement 1:
indicates that x+y =840, therefore x/x+y = x/840 we cannot answer the question as X is unknown.
Statement 2:
Indicates that: 75% of x+y applied for the college thus-
72% of X and 80 % of Y = 75% of x+y
72/100 * X + 80/100*y = 75/100 (x+y)
from this we can get x in terms of y and thus we can calculate x/x+y
So statement 2 is enough to solve the problem.