1. **State the problem:** We have a spinner divided into 10 equal sectors: 4 red, 3 blue, 2 yellow, and 1 green. 2. **What is asked?** Find the probability that the spinner lands on a blue sector when spun once. 3. **Formula for probability:** $$\text{Probability} = \frac{\text{Number of favorable outcomes}}{\text{Total number of outcomes}}$$ 4. **Apply the formula:** - Number of favorable outcomes (blue sectors) = 3 - Total number of outcomes (total sectors) = 10 So, $$\text{Probability} = \frac{3}{10}$$ 5. **Simplify the fraction if possible:** $$\frac{3}{10}$$ is already in simplest form. 6. **Interpretation:** There is a 3 out of 10 chance the spinner lands on blue. **Final answer:** $$\boxed{\frac{3}{10}}$$