Question 815953
The third side must be larger than 10-5 = 5 units. 


Let x be the third unknown side. So if the third side must be larger than 5 units, then we can say x > 5.


The perimeter of the triangle is


P = s1 + s2 + s3


P = 5+10+x


P = 15+x


Now if x > 5, then this means that 15+x > 20 (add 15 to both sides of the original inequality)


So the perimeter must be larger than 20 units. If the perimeter is an integer (or whole number), then the smallest it can be is <font color="red">21 units</font>.