Question

average of 3 numbers is 9.if average of first two number be 12,then find the third number

Answer 1

The answer is 3 .
Regard A , b and c as some numbers and equate them .

Answer 2

consider three numbers as x,y,z given that:. x+y+z/3=9 hence x+y+z=9×3=27 x+y+z=27...............1
given that x+y/2=12 hence x+y=12×2=24. x+y=24..................2 third no.is z. from 1 and 2,. 24+z=27. z=27-24. z=3. hence the third number is 3..ok