say speed of X is x miles/hr
speed of Y is y miles.hr
speed of Z is z miles/hr
Say AB=d miles.
then time to reach M by X and Y is same. distance covered by x is d+20; by Y is 20.
Hence, x/y= (d+20)/20 ...........(1)
to reach N, distance travelled by Y is 20 and Z travels d+40. h...