a pulse was created in a slinky of length 4m by group of students .they observed that it returned,after ,reflection, at the point of creation 6times in10 seconds and calculated the speed as ?

we know that speed is given as distance / time

here,

distance = 4m

time = the time taken by the pulse to travel 1 to and fro.

which will be time taken by n number of to and fro / n.

here pulse travels 6 to n fro in 10 sec.  (n = 6)

time = 10/6 = 1.66 s

so,

speed =  4/1.6  =  2.5 m/s