Question

Which set of lengths CANNOT form a triangle? A. 16, 18, 20 B. 13, 14, 23 C. 8, 6, 5 D. 14, 20, 3

Answer 1

just a quick addition to the great reply above, Check the picture below.

notice on the picture atop, if we lay the 14 side on top of the 20 side, the slack is just 6, however we get a flat-line not a triangle, so the red side must be greater than 6 for that.

on the picture below, if we had the two small sides to open to a flat line, they add up to 17, no way to fit a side of 20 there, so the red side must be less than 17.

Answer 2

D. 14, 20, 3 Cannot for a triangle

Step-by-step explanation:
To form a triangle any two of the lengths must always be greater than the third when added together, so 16 + 18 will always be greater than 20 and 18 + 20 > 16
While with D, 14 + 3 is less than 20 so it cannot form a triangle, and is the answer.
Hope this helps!