11. The diagram shows four equilateral triangles with sides of lengths $1,2,3$ and 4. The area of the shaded region is equal to $n$ times the area of the unshaded triangle of side-length 1 .
What is the value of $n$ ?
A 8
B 11
C 18
D 23
E 26
11. E Let the area of the equilateral triangle of side 1 be $A$. If similar figures have sides which are in the ratio $k: 1$, then the ratio of their areas is $k^{2}: 1$. So the areas of the triangles with sides 2 , 3,4 are $4 A, 9 A, 16 A$ respectively.
So, as shown in the diagram, the total shaded area is $3 A+8 A+15 A=26 A$. Therefore $n=26$.