Question

Which set of three numbers could be the side lengths of a triangle?

Answer 1

For any triangle, the third side must be greater than difference of two sides and less than the sum.

Let the third side be x.

for 2, 4           x > 2,     x < 6.      
8 does not fit in, so 2,4, 8 can't form triangle

for 3, 5           x > 2,     x < 8.      
7 does fit in, so 3,5, 7 can form a triangle.

Testing the others in the same, doesn't form the sides of a triangle.

So only set B 3,5,7 could be the side lengths of a triangle.

Answer 2

B is the answer. The sum of two triangle legs should be more than the legth of the third.