Four women must cross a bridge over a deep ravine in enemy territory in the middle of the night, treacherous bridge will hold on two women at once and it's necessary to carry a lantern while crossing. (person must stay together while crossing but may return alone) . one of the woman requires five mins for the trip across, one takes ten minu, a third requires 20 and the last takes 25 minutes (each of them can walk slower if necessary but no faster). unfortunately they only have one lantern among them. how can they make the cro

Ok, this is usually a trial and error question and it is supposed to be fun.
I believe you want the four women to cross the bridge in the least possible time before the bridge collapses.

The solution is as follows:
1- The 5-minute lady and 10-minute lady cross the bridge
    (the total time will be 10 minutes)
2- The 5-minute lady returns
    (the total time will be 5 + 10 = 15 minutes)
3- The 20-minute lady and 25-minute lady cross
    (the total time will be 15 + 25 = 40 minutes)
4- The 10-minute lady returns 
    (the total time will be 10 + 40 = 50 minutes)
5- The 5-minute lady and 10-minute lady finally cross
    (the total time will be 10 + 50 = 60 minutes)

The last one to cross should step aside from the bridge as quickly as possible before the bridge collapses.

Xis equal to three

It would be 0 at least it should be