Question

If average of first 7 numbers is 50 and first 3 numbers is 40 and last 3 numbers is 60. What is the middle number

Answer 1

let the no's are a,b,c,d,e,f and g
then
a+b+c+d+f+g /7 =50
= a+b+c+d+e+f+g = 350-------------------eq.1

=a+b+c /3 = 40
=a+b+c = 120--------------------eq.2

and also
=e+f+g /3 = 60
=e+f+g = 180 ----------------------eq.3

now from eq.2 and eq.3 put value in eq.1

so
=120 + d + 180 = 350
= d= 350-180-120
= d=50
hence middle no is 50