sebuah persegi panjang mempunyai perbandingan panjang dan lebarnya 3 banding 5 jika keliling 160 cm Tentukan luasnya

160 = 2(p+l)
160 = 2(3x+5x)
160 = 2(8x)
160 = 16x
10 = x

Luas = p × l
= 3x × 5x
= 3(10) × 5(10)
= 30 × 50
= 1500

p : l = 3 : 5
Misal :
p = 3x
l = 5x

Keliling = 160 cm
2p + 2l = 160
2 (3x) + 2 (5x) = 160
6x + 10x = 160
16x = 160
x = 160/16
x = 10 cm

p = 3x = 3 (10) = 30 cm
l = 5x = 5 (10) = 50 cm

Luas persegi panjang
= p x l
= 30 x 50
= 1500 cm²