Question

Perbandingan panjang, lebar, dan tinggi sebuah balok berturut-turut 5 : 3 : 2. jika volume balok tersebut 810 cm3, maka luas permukaannya adalah ?

Answer 1

P:L:T =5:3:2 = 5a:3a:2a

Px LxT = Volume
5ax3ax2a = 810
30a³ = 810
a³ = 810/30 = 27
a =∛27 = 3

P = 5a= 5(3)= 15
L= 3a= 3(3) =9
T = 2a= 2(3)= 6

LP = 2(PL +PT+LT)
     = 2(15*9 +15*6+9*6)
     = 2 (135+90+54)
    = 2(279)
    = 558 cm²

Answer 2

Volume = p x l x t
810      = 5a x 3a x 2a
810      = 30a³
a³        = 27
a         = ∛27
a         = 3

p = 5a = 5(3) = 15 cm
l = 3a = 3(3) = 9 cm
t = 2a = 2(3) = 6 cm

Maka;
Lp = ( 2 x p x l ) + ( 2 x p x t ) + ( 2 x l x t )
Lp = ( 2 x 15 x 9 ) + ( 2 x 15 x 6 ) + ( 2 x 9 x 6 )
Lp = 270 + 180 + 108
Lp = 558 cm²