Answer: The length of the third side is greater than 5 and less than 15 units.
Step-by-step explanation: Given that the lengths of two sides of a certain triangle are 5 and 10 units.
We are to find the length of the third side of the triangle.
Let x represents the length of the third side of the given triangle.
We know that the sum of the lengths of two sides of a triangle is always greater than the length of the third side, so we must have


and

From inequalities (i), (ii) and (iii), we get

Thus, the length of the third side is greater than 5 and less than 15 units.