Question

on decreasing the radius of circle by 30%its area is decreased by howmuch

Answer 1

Area of a circle is $\pi x^{2}$ 
original area = pi*r^2
now as suggested the radius is reduced by 30%
 newr = r - rx30/100
r(1-0.3) = 0.7r
calculating the area with the new radius gives pi*49r^2
original area = pi*r^2
loss in area  = modified - original/original
(49*pi*r^2 - pi*r^2 / pi*r^2)*100
(-51pi*r^2 /pi*r^2)*100
= -51% (since loss, the result is negative)
implies there would be a 51% loss in the area