20. The diagram shows five congruent right-angled isosceles triangles. What is the total area of the triangles?
A $25 \mathrm{~cm}^{2}$
B $30 \mathrm{~cm}^{2}$
C $35 \mathrm{~cm}^{2}$
D $45 \mathrm{~cm}^{2}$
E $60 \mathrm{~cm}^{2}$
20. D Consider one of the right-angled isosceles triangles as shown.
The longest side is $(30 / 5) \mathrm{cm}=6 \mathrm{~cm}$. The triangle can be divided into two identical right-angled isosceles triangles with base $3 \mathrm{~cm}$ and hence with height $3 \mathrm{~cm}$. Therefore the area of each of the original triangles is $\left(\frac{1}{2} \times 6 \times 3\right) \mathrm{cm}^{2}=9 \mathrm{~cm}^{2}$. Hence the total shaded area is $5 \times 9 \mathrm{~cm}^{2}=45 \mathrm{~cm}^{2}$.