If there is a room with 15 women, each woman shakes the hands of 8 men and each man shakes the hands of 6 women, how men there are in the room?
So far I wrote this: Women group A=$(v_1...,v_m)$ men group B=$(u_1....,u_n)$ $G=(A,B,E) $ , $|A|=m=15 $ ,$|B|=n$ and $N(u_n)=6$,$N(v_n)=8$ is it correct? and i so how can i move on to solve it?
If there are $n$ men then $15\times8$ and $n\times 6$ both equal the number of handshakes that involve a man and a woman.
That implies $n=20$.