average

[fecoupefe]

The average of five numbers is 6. If one of the five numbers is removed,the average of the four remaining numbers is 7. What is the value of the number that was removed?

 

[arthur ohlsten]

let the 5 numbers be a,b,c,d,e

then:
[a+b+c+d+e] /5=6 multiply both sides by 5
eq 1) a+b+c+d+e=30

but we know:
[a+b+c+d]/4=7 multiply both sides by 4
eq 2) a+b+c+d=28

substitute 28 for a+b+c+d into eq.1
28 + e=30
e=2 answer

Or subtract eq 2) from eq 1)

Arthur

 

[fecoupefe]

Thank u Arthur for your clear explanation in explaining the problem!

 

[arthur ohlsten]

Your more than welcome.
I hope you find math as enjoyable as I have. I did graduate work in math 54 years ago and I still enjoy doing math.
Good luck with your studies
Arthur

 

[fecoupefe]

Thank you for your encouraging words.

I wish math came naturally but it doesn't and to explain it to a 10 yr old doesn't help either!