Diketahui sebuah kerucut panjang jari jari alasnya 10 cm dan vol 200 pi cm3,apabila t kerucut di perkecil 1/2 kalinya,hitunglah:

V = 1/3 phi x r2 x t
200 phi = 1/3 phi x r2 (phi coret)
200 = 1/3 x 100 x t
200 x 3 = 100 t
600 = 100 t
tinggi sebelun diperkexil = 600 : 100
= 6 cm
volume = 1/3 x phi x r2 x 1/2 t
= 1/3 x phi x 100 x 1/2 x 6
= 1/3 x 100 x 3 x phi
= 100 phi