Question

william recorded the grade - level and instrument of everyone in the middle school school of rock below. seventh grade students: instrument # of students guitar 9 bass 11 drums 9 keyboard 11 eighth grade students: instrument # of students guitar 3 bass 3 drums 8 keyboard 6 based on these results, express the probability that a seventh grader chosen at random will play the keyboard as a fraction in simplest form.

Explanation:

Step1: Find total number of seventh - graders

Add the number of students for each instrument in seventh grade. $9 + 11+9 + 11=40$.

Step2: Find number of seventh - graders who play keyboard

The number of seventh - graders who play keyboard is 11.

Step3: Calculate the probability

The probability $P$ that a randomly chosen seventh - grader plays the keyboard is the number of seventh - graders who play keyboard divided by the total number of seventh - graders. So $P=\frac{11}{40}$.

Answer:

$\frac{11}{40}$