Question

average of 3 number is 7 and average of two of them is 4 then the 3rd number is

Answer 1

average of (a,b,c) =7
it means (a+b+c)/3=7.... a+b+c=21
given that (a+b)/2=4... a+b=8
so the third number is c=13

Answer 2

let the three no. be x1, x2, x3
no. of event=n=3
average(mean)=€xi/n=(x1+x2+x3)/3=7
€xi=7×3=21
let the no. excluded be a
then
(21-a)/2=4
21-a=8
a=21-8=13
hence third no.is 13