141k views
0 votes
A class of 40 students took a math test 18 of the students had a weighted average of 80. The other students had a weighted average of 70. What is the average score of the whole class? A) 74 B) 74.5 C) 76 D) 76.5​

1 Answer

0 votes

Answer: B) 74.5

==========================================================

Step-by-step explanation:

Average = (sum of scores)/(number of scores)

We can turn that equation into symbolic form to say

A = S/n

We're told that "18 students had an average of 80" (paraphrased) which means,

A = S/n

80 = S/18

80*18 = S

S = 1440

Those 18 students' scores add up to 1440.

For the other group of 40-18 = 22 students, their scores add to

S = A*n

S = 70*22

S = 1540

Overall, everyone's scores add up to 1440+1540 = 2980

Divide this over the number of people in class (40) to get the final answer

2980/40 = 74.5

--------------------------------------------

Here's an alternative way to compute the answer

(18/40)*80 + (22/40)*70 = 74.5

This works because 18/40 of the class got an average of 80 while the remaining 22/40 of the class got an average of 70.

User King Chan
by
7.8k points

No related questions found

Welcome to QAmmunity.org, where you can ask questions and receive answers from other members of our community.

9.4m questions

12.2m answers

Categories