Question

Which of the following sets of lengths could not be the side lengths of a triangle?

Answer 1

To find out if the three side lengths can create a triangle, the three smaller lengths must be greater than the longer length.

$\bf~Option~A$

$\sf~3~meters,5~meters,7~meters$

$\sf3+5=8>7$

So this can create a triangle.

$\bf~Option~B$

$\sf1~yard,1.25~yards,1.5~yards$

$\sf1+1.25=2.25>1.5$

So this can create a triangle.

$\bf~Option~C$

$\sf5~inches,10.5~inches,17~inches$

$\boxed{\sf5+10.5=15.5$

So this cannot create a triangle.

$\bf~Option~D$

$\sf15~millimeters,18~millimeters,30~millimeters$

$\sf15+18=33>30$

So this can create a triangle.

Therefore, your answer is Option C.