How far from the Middle must the man stand to balance the boy

[mlavio829]

Hi,
Could anyone please help me with this question:
A man with mass of 80 kg wants to balance a 40 kg boy who is standing at the end of the board.
If the board is uniform and has a mass of 20 kg how far from the middle in meters, x, must the man stand
so that he and the boy balance each other?

Homework Equations

-centre of mass?

The Attempt at a Solution

answer is 1.6 but i don't know how to get to it


Any help would be greatly appreciated.
Thanks
Michael

 

[mgb_phys]

I think you have slightly miss-stated the question.
If the board was balanced at the middle then it's weight wouldn't matter and the man would have to stand half way between the end and the middle. Since you aren't given the actual length of the board then the answer would have to be in terms of the length.