An equilateral triangle of side length 10 is completely filled in by non-overlapping equilateral triangles of side length 1 . How many small triangles are required?

**Answer Choices**

A. 10

B. 25

C. 100

D. 250

E. 1000

An equilateral triangle of side length 10 is completely filled in by non-overlapping equilateral triangles of side length 1 . How many small triangles are required?

**Answer Choices**

A. 10

B. 25

C. 100

D. 250

E. 1000