To find out the amount of 1/2 yard pieces that Isaac can cut from a 5-yard long length of rope, all we need to do is divide 5 by 1/2 to get our answer (since that is what he is doing, dividing a 5-yard long piece of rope into 1/2 yard long pieces).
5 / (1/2) = 10
Isaac can cut 10 1/2-yard pieces of rope from the original rope.
Hope that helped! =)
