Question

the avg of 5 numbers is 18.4.the avg of of the first 3 numbers is 12 and the avg of the last 3 numbers is 30. find the third no.

Answer 1

let the no.s be x,y,z,a,b.
given, (x+y+z+a+b)/5 = 18.4
or x+y+z+a+b= 18.4*5 =92.............................................(1)

now given that the avg of frst 3 is 12.
ie (x+y+z)/3 = 12
or x+y+z = 36.....................................................................(2)

and the avg of lst 3 nos is 30.
ie (z+a+b )/3 =30
or z+a+b = 90............................................................(3)

adding 1 & 2
x+y+z+z+a+b = 126...................................................(4)

substituting 1 in 4:
z+92 = 126
or z=126-92
z=34.

Answer 2

the third number is 34............