Question

there are 8 twelve - year - olds and 12 thirteen - year - olds in mr. rossis class. one student will be chosen randomly to represent the class at a conference of seventh - grade students. what is the probability that the representative will be a thirteen - year - old?

Explanation:

Step1: Calculate total number of students

$8 + 12=20$

Step2: Calculate probability of choosing a thirteen - year - old

The number of thirteen - year - olds is 12. Probability $P=\frac{\text{Number of favorable outcomes}}{\text{Total number of outcomes}}=\frac{12}{20}=\frac{3}{5}$

Answer:

$\frac{3}{5}$