I have two piles of marbles. Every round I select the pile with the least marbles, and double it, taking the necessary marbles from the other pile. If I start with 1 and 24, will either pile at some point be empty? What if it's 1 and 25, or 1 and 23?
You will only be able to reach 0 on the largest pile when the number of marbles is (2^k-1) Consider for instance that case when you have 1 and 15 marbles You will get this sequence of events: 1 15 2 14 4 12 8 8 0 16 This happens because by the time the smallest pile becomes larger than the other one you have subtracted 1+2+4+...2^k = 2^(k+1)-1. If you start off with more than 2^(k+1)-1 you can see there is no way you get one pile to zero.
Do research on the position and the organization in advance, understand well about the organization (products/goal) and the position (functionality and tasks). More importantly, it is always about personality, the team care about whether you can fit in the team or not.
First part - 5 minutes, really simple questions. But you have to be a calculator to answer all of them. Second part - 10 minutes. More difficult questions, the tactic is to skip hard questions and answer easiest part first, for example 120/6 or 59 * 5. Third part includes "real life questions", such as if 3/5 of the X is 7 what is 11/6 of X. This part also can include questions about rectangle or circle area, or progression questions(1+2+....+49+50). The last part contains difficult questions and for that one you have to apply arithmetic rules. Example, 5*2*7*2*2*5 you have to calculate 5*7*2 = 70, 2*5 = 10, then to calculate final answer 70*10*2