Suppose someone tells you that she has a triangle with sides having lengths 3.5, 4.5 and 5.5 yards. is this a right triangle?

I don't know.
Let's find out.
If it IS a right triangle, then . . .

    (square of the shortest side)
plus
    (square of the medium side)
adds up to
     (square of the longest side).

Shortest side = 3.5 .  Its square is  (3.5)²  =  12.25
Medium side = 4.5 .  Its square is  (4.5)²   =  20.25
(square of the shortest side) + (square of the medium side) =  32.5 .

Longest side = 5.5 .  Its square is  (5.5)²   =  30.25 .

  30.25  is NOT equal to  32.5 .

  So this is NOT a right triangle.