SS1 Math direct variation

a) Let y = kx^2
if x is increased by 20% ,
k(1.2x)^2
= k(1.44x^2)
= 1.44 kx^2
= 1.44y
i.e. the percentage change in y is (1.44 - 1) x 100% = + 44%
b) Let y = kx^2
if x is decreased by 40%,
k(0.6x)^2
= k(0.36x^2)
= 0.36 kx^2
= 0.36 y
.e. the percentage change in y is (0.36 - 1) x 100% = - 64%