I think a lot of companies use brain teasers or math problems to test general mental aptitude, whether it works or not is under serious debate, but in my opinio

I think a lot of companies use brain teasers or math problems to test general mental aptitude, whether it works or not is under serious debate, but in my opinion that's the right thing to test for (if it's even possible). The reason is smart people can figure out git, or databases, or objective-c, or whatever, in a fairly short amount of time. For example, my co-founder learned objective C off free online video tutorials and built an iOS app (talking an app with serious firepower and back-end transaction logic) from start to end by himself in less than 3 weeks. That's why we're not as concerned about what you know right now as what it's possible for you to learn in 3 more week.