Simple puzzle.....

/\ In this triangle, there are nine (9) little
/_\ triangles. Then there are three (3)
/\ /\ triangles which are larger (containing 4 little ones)
/_\/_\ and one (1) largest (containing all 9).
/\ /\ /\
/_\/ \/_\ 9+3+1 = 13 triangles.

so two big triangles means 26 such triangles
i found a little formula for determining the number of triangles in such a arrangement

b = Number of triangles in the base
l = Number of little triangles
f = Next largest triangle (contains 4 small triangles)
n = Next largest triangle (contains 9 small triangles)
s = Next largest triangle (contains 16 small triangles)
T = Total number of triangles

b l f n s T
1 1 0 0 0 1
2 4 1 0 0 5
3 9 3 1 0 13
4 16 7 3 1 27

I also think there are 20 triangles! :-)
2 Big ones
2 x 3 Medium Size Ones
12 Small Ones

first count all small triangles , i.e.=12

Then count the triangles containing 4 small triangles

six corners so this type 6

Now count triangles containing 9 small triangles

this type = 2

so total triangles = 12 +6+2 =20

yup 20 triangles