What you needFive round objects of very different sizes: a coin, a bangle, a cup, a plate, a bucket lid. A piece of string and a ruler.
MethodWrap string once round each object and straighten it against a ruler to get the circumference. Measure straight across the widest part to get the diameter. Divide one by the other.
The pointChoose objects of wildly different sizes on purpose, so that the last column coming out the same is genuinely surprising.
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