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Problem 175

Combinatorics Difficulty 1.5 Multiple choice CEMC Gauss (Grade 7) · Canada · 2019

A circular spinner is divided into 8 equal sections, as shown.

An arrow is attached to the centre of the spinner. The arrow is spun once. What is the probability that the arrow stops in a section containing a prime number that is odd?

Pick one

Official solution

On the spinner given, the prime numbers that are odd are $3,5$ and 7.

Since the spinner is divided into 8 equal sections, the probability that the arrow stops in a section containing a prime number that is odd is $\frac38$ .

Source: CEMC, University of Waterloo, licensed CC-BY-NC-4.0. Statement reproduced verbatim; metadata (topic, difficulty, ordering) added by this project.