No. of equilateral triangles required to completely fill a bigger equilateral triangle $\triangle ABC$ is equilateral with side length=2.1cm
Smaller equilateral triangles with side length=1cm are placed over $\triangle ABC$ so that it is fully covered. Find the minimum number of such small triangles.
I am not getting it. How is it possible to completely fill with such dimensions?

Six triangle suffice (three in the corners and three in the middle of the sides).
It is not possible with less than six triangles:
Let $D$ be the midpoint of $AB$, $E$ the midpoint of $BC$, $F$ the midpoint of $CA$.
Then the distance between any two of the points $A,B,C,D,E,F$ is $\ge1.05>1$, hence no two of them can be covered by the same side-1-triangle.
