



 
Hi Janna, The circumference of a circle of diameter $d$ inches is $\pi \; d$ inches and you want half of this. In my diagram above the brown rope is formed in a semicircle but the length of the outside of the semicircle is larger than the length of the inside of the semicircle. To make sure the rope reaches around the semicircle you should take the diameter to be $d + 2\times t$ inches where $t$ is the thickness of the rope. Penny  


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