Zifo RnD Solutions Engineer interview questions

i just have a vague idea on the questions... On a farm, there are chickens and sheep. You are given the total number of heads and legs. For example, if there are 10 heads and 28 legs, how many chickens and sheep are there? an hour glass question, i assume this is the one... Given two hourglass of 4 minutes and 7 minutes, the task is to measure 9 minutes. One family wants to get through a tunnel. Dad can make it in 1 minute, mom in 2 minutes, son in 4 and daughter in 5 minutes. No more than 2 persons can go through the tunnel at one time, moving at the speed of the slower one. Can they all make it to the other side if they have a torch that lasts only 12 minutes and they are afraid of the dark?​