Two sides of a triangle are 10mm and 7mm. Determen the length of the third side from the chocies given 5mm, 1mm, 20mm, and 2mm.

To determine the length of the third side of the triangle, we can use the triangle inequality theorem, which states that the sum of the lengths of any two sides of a triangle must be greater than the length of the third side.

In this case, the two given sides are 10mm and 7mm. Let's calculate the range for the possible lengths of the third side:
- For 5mm: 10 + 7 > 5, so 5mm is a possible length.
- For 1mm: 10 + 7 > 1, so 1mm is a possible length.
- For 20mm: 10 + 7 < 20, so 20mm is not a possible length.
- For 2mm: 10 + 7 > 2, so 2mm is a possible length.

Therefore, the possible lengths of the third side are 5mm, 1mm, and 2mm.