how to find how many ridges a 10 p coin has?

Question

What do we measure and how do we work it out?

Answer 1

this is physics?

measure the circumference C of the coin
measure the distance D between two ridges

number of ridges = C/D

For example, if the coin is 5 cm around, and each ridge occupies 1 mm (.1 cm), then there are 5/.1 = 50 ridges.

Answer 2

You need to add one as there is one extra ridge compared to the number of spacings between ridges