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### Course: Algebra (all content)>Unit 2

Lesson 12: Old school equations with Sal

# Averages

We can calculate an average by adding up all the numbers in a group and dividing by the number of numbers. We can also use algebra to solve problems involving averages, and figure out how well we need to do on exams to get a good grade in a class. Created by Sal Khan.

## Want to join the conversation?

• So you just add all the numbers together and then divide by how ever many numbers there are so like 2+4+6+8=20 then divide 20/4=5 so 5 would be the average of 2,4,6,8 right?
• Yep. Add all the numbers, divide the total by the amount of numbers you added, and you have the answer.
• During of the how did he get 7.25
• He added the 4 numbers, divided it by however many numbers there were (4) then found 7.25. Doing the division he ran into 7 remainder of 1 so he added a decimal and two invisible zeros.
• What is 1/3= .33333333333333333333? Is this correct?
• how can i find the fourth number if given three numbers and the average of the four numbers?
• Try writing out the formula for the average, using a letter for the unknown number. Then see if you can rearrange it to make the letter that you want to know the subject.
• you ran 8 miles? holy cow that's awesome. Someone please reply to this.
• I'm confused, I came here for weighted averages, but it's not coming out, what is a weighted average?
(1 vote)
• At , why did you multiply "88" by "5"? and where did the "5" under "4 . 84 + x" go?
• Following inexactly to Sal's example, I tried to average 1, 3, 7. 1+3+7=11, but (assuming since Sal averages four numbers, he puts 4 here, I did 3, so I put 3) how would I write down the fourth three that goes into 11? 2/3, or 0.65?
(1 vote)
• I don't know exactly what you are saying but here is how you solve your problem.

1+3+7=11

11/3=3.666666666

Answer: 3.6 repeating (You would put a dash above the six)

Hope this helps! =)
• A family consists of 2grandparents,2parents,3grand children.the average age of grandparents is 65years that of parents is 40years&that of grand children is 7years.find the average age of the family
(1 vote)
• Continuing on from what Victor has,
=> (130+80+21)/(7)
=> 231/7 = 33.
The average age of the family is 33.
(1 vote)
• -3n=30
not sure how to do this type of question
(1 vote)
• This is a fairly simple problem. All you need to do is divide both sides of the equation by -3, and you will see that n = -10

Good luck!
(1 vote)