Question

∆ABC ∼ ∆DEF and the perimeters of ∆ABC and ∆DEF are 30 cm and 18 cm respectively. If BC = 9 cm, then EF = ?
(a) 6.3 cm
(b) 5.4 cm
(c) 7.2 cm
(d) 4.5 cm

Answer 1

(b) 5.4 cm

∆ABC ∼ ∆DEF

Therefore,

$$\begin{gathered} \frac{\mathrm{Perimeter}\left(△ABC\right)}{\mathrm{Perimeter}\left(△DEF\right)}=\frac{BC}{EF} \\ \Rightarrow \frac{30}{18}=\frac{9}{EF} \\ \Rightarrow EF=\frac{9\times 18}{30}=5.4\mathrm{cm} \end{gathered}$$