There is a single spinning disc with a total of seven sectors in three different colours. Three sections are coloured red, two are coloured yellow, and two are coloured blue. What is the probability of getting a red section when the wheel is spun once?

The probability of an event is given as:

Probability of an event = $\frac{\mathrm{Outcomes} \mathrm{of} \mathrm{an} \mathrm{event}}{\mathrm{Total} \mathrm{possible} \mathrm{outcomes}}$

There is a total of 7 sections of the wheel. Therefore, the total number of possible outcomes is 7. 
There are 3 red sections on the wheel. 

$\therefore$The probability of getting a red section = $\frac{3}{7}$