Find the area of the circle inscribed in a square

1) Find the area of the circle inscribed in a square having diameter as 16sqrt(2)
2) Given mean of three numbers 2x,7x, and x^2 is 12. find the range of the numbers.
here i got x=3 and -12 how can we find the range?
3) Which of the following can not be necessarily true?

c) a^2+b^2=c^2
d) atleast two are acute angles
for this C and B are not necessarily true. am i correct?
4) Given (x-3)/x-1)<0 where x>1 find x?
5) If three sides of a quadrilateral are equal and are of the x cm, then find the perimeter of
quadrilateral.
here the fourth angle must be equal to x. So it is 4x.is it correct?
6) In a group 7 out of 15 students admitted in a university and one of them absent everyday. If 315
students were admitted last month, how many students were not absent at all?
7) If a person 'A' did 1/5th of the work and another 'B' did 1/6th of the remaining work. what is the
work still left?

8) A computer system digit code has 5 digits in that 'x' repeats once, y repeats twice and z repeats
twice system accepts this code xyzyz and yyxzz
colA:the number possible for the system code
colB:xxx(some value)