The shortest one!
There are three pillars, X, Y and Z of different heights. Three spiders A, B and C start to climb on these pillars simultaneously. In one chance, A climbs on X by 5cm, but slips down 1cm. B climbs on Y by 6cm, but slips down 3cm. C climbs on Z by 7cm, but slips down 2cm. If each requires 50 chances to reach the top of the pillar, what is the height of the shortest pillar? (in cm)