Question 369336
x+(x+1)+2 = 20
2x + 3 = 20, or 2x = 17, no integer solution.
x+x+2 = 20,
2x  = 18, or x = 9.  Therefore you need 2*9 = 18 1 inch equilateral triangles.(9 at the top, 9 at the bottom.)